Communication method and device in mobile communication system

ABSTRACT

The present disclosure relates to a communication technique for converging, with an IoT technology, a 5G communication system for supporting a higher data transmission rate beyond a 4G system, and a system therefor. The present disclosure may be applied to intelligent services, such as smart homes, smart buildings, smart cities, smart cars or connected cars, health care, digital education, retail, and security and safety related services, on the basis of 5G communication technologies and IoT-related technologies. The present disclosure relates to a method for a terminal in a communication system and a device for performing same, the method comprising the steps of: receiving, from a higher layer device, information indicating packet data convergence protocol (PDCP) data recovery; identifying first data associated with transmission for the PDCP data recovery, from data which have been stored in a signaling radio bearer (SRB) before the information is received; and transmitting the first data to a lower layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 17/250,312,filed Dec. 31, 2020, now U.S. Pat. No. 11,337,125 issued May 17, 2022,which is a 371 of International Application No. PCT/KR2019/008025 filedon Jul. 2, 2019, which claims priority to Korean Patent Application No.10-2018-0076639 filed on Jul. 2, 2018, the disclosures of which areherein incorporated by reference in their entirety.

BACKGROUND 1. Field

The disclosure relates to a method and an apparatus for preventing dataloss due to handover within a BS in a next-generation mobilecommunication system.

Further, the disclosure relates to a method and an apparatus forsupporting a ultra-reliable low latency communication (URLLC) service toa UE operating in a radio resource control (RRC)-connected mode in anext-generation mobile communication system and, more particularly, to amethod and an apparatus for determining a modulation and coding scheme(MCS) of a UE operating in an RRC-connected mode.

2. Description of Related Art

To meet the demand for wireless data traffic having increased sincedeployment of 4G communication systems, efforts have been made todevelop an improved 5G or pre-5G communication system. Therefore, the 5Gor pre-5G communication system is also called a “Beyond 4G Network” or a“Post LTE System”. The 5G communication system is considered to beimplemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, soas to accomplish higher data rates. To decrease propagation loss of theradio waves and increase the transmission distance, the beamforming,massive multiple-input multiple-output (MIMO), full dimensional MIMO(FD-MIMO), array antenna, an analog beam forming, large scale antennatechniques are discussed in 5G communication systems. In addition, in 5Gcommunication systems, development for system network improvement isunder way based on advanced small cells, cloud radio access networks(RANs), ultra-dense networks, device-to-device (D2D) communication,wireless backhaul, moving network, cooperative communication,coordinated multi-points (CoMP), reception-end interference cancellationand the like. In the 5G system, hybrid FSK and QAM modulation (FQAM) andsliding window superposition coding (SWSC) as an advanced codingmodulation (ACM), and filter bank multi carrier (FBMC), non-orthogonalmultiple access (NOMA), and sparse code multiple access (SCMA) as anadvanced access technology have also been developed.

The Internet, which is a human centered connectivity network wherehumans generate and consume information, is now evolving to the Internetof things (IoT) where distributed entities, such as things, exchange andprocess information without human intervention. The Internet ofeverything (IoE), which is a combination of the IoT technology and thebig data processing technology through connection with a cloud server,has emerged. As technology elements, such as “sensing technology”,“wired/wireless communication and network infrastructure”, “serviceinterface technology”, and “security technology” have been demanded forIoT implementation, a sensor network, a machine-to-machine (M2M)communication, machine type communication (MTC), and so forth have beenrecently researched. Such an IoT environment may provide intelligentInternet technology services that create a new value to human life bycollecting and analyzing data generated among connected things. IoT maybe applied to a variety of fields including smart home, smart building,smart city, smart car or connected cars, smart grid, health care, smartappliances and advanced medical services through convergence andcombination between existing information technology (IT) and variousindustrial applications.

In line with this, various attempts have been made to apply 5Gcommunication systems to IoT networks. For example, technologies such asa sensor network, machine type communication (MTC), andmachine-to-machine (M2M) communication may be implemented bybeamforming, MIMO, and array antennas. Application of a cloud radioaccess network (RAN) as the above-described big data processingtechnology may also be considered an example of convergence of the 5Gtechnology with the IoT technology.

In a next-generation mobile communication system, various structures ofBSs can be implemented and various radio access technologies maycoexist. The technical problems to be solved by embodiments of thedisclosure are to provide a method of preventing data loss when a UEchanges a radio link to another cell or another BS because the UEperforms a handover or changes a bearer type.

Further, the technical problems to be solved by embodiments of thedisclosure are to provide a method and an apparatus for supporting URLLCservice.

SUMMARY

In accordance with an aspect of the disclosure, a method of a UE in acommunication system includes: receiving information indicating packetdata convergence protocol (PDCP) data recovery from a higher layerdevice; identifying first data related to transmission for the PDCP datarecovery among data stored in a signaling radio bearer (SRB) beforereceiving the information; and transmitting the first data to a lowerlayer.

In accordance with another aspect of the disclosure, a UE in acommunication system includes: a transceiver; and a controller connectedto the transceiver and configured to perform control to receiveinformation indicating packet data convergence protocol (PDCP) datarecovery from a higher layer device, identify first data related totransmission for the PDCP data recovery among data stored in a signalingradio bearer (SRB) before receiving the information, and transmit thefirst data to a lower layer.

The technical problems to be solved by embodiments of the disclosure arenot limited to the above-mentioned technical problems, and technicalproblems which have not been mentioned may be clearly understood bythose skilled in the art on the basis of the following description.

According to embodiments of the disclosure, it is possible to provide amethod of performing a handover without any data loss by supporting adetailed method of preventing data loss which may be caused by ahandover of a UE in a next-generation mobile communication system.

Further, according to embodiment of the disclosure, it is possible toprovide a method of determining a modulation and coding scheme forsupporting URLLC service.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a structure of an LTE system according to anembodiment of the disclosure;

FIG. 1B illustrates a structure of a wireless protocol in the LTE systemaccording to an embodiment of the disclosure;

FIG. 1C illustrates a structure of a next-generation mobilecommunication system according to an embodiment of the disclosure;

FIG. 1D illustrates a structure of a wireless protocol of thenext-generation mobile communication system according to an embodimentof the disclosure;

FIG. 1E illustrates a procedure in which a UE performs an RRC connectionconfiguration with a BS when the UE establishes a connection with anetwork in a next-generation mobile communication system according to anembodiment of the disclosure;

FIG. 1F conceptually illustrates a handover between BSs in anext-generation mobile communication system according to an embodimentof the disclosure;

FIG. 1G conceptually illustrates a procedure of changing or releasingone BS of a split bearer or one radio access technology for a UE usingthe split bearer through two BSs or two radio access technologies in anext-generation mobile communication system according to an embodimentof the disclosure;

FIGS. 1HA, 1HB, and 1HC illustrate a structure of a BS which can beimplemented in a next-generation mobile communication system accordingto an embodiment of the disclosure;

FIG. 1I illustrates a UE operation according to an embodiment of thedisclosure;

FIG. 1J illustrates a configuration of a UE according to an embodimentof the disclosure;

FIG. 1K illustrates a configuration of a BS according to an embodimentof the disclosure;

FIG. 2A illustrates a structure of an LTE system according to anembodiment of the disclosure;

FIG. 2B illustrates a structure of a wireless protocol in the LTE systemaccording to an embodiment of the disclosure;

FIG. 2C illustrates a structure of a next-generation mobilecommunication system according to an embodiment of the disclosure;

FIG. 2D illustrates a structure of a wireless protocol of thenext-generation mobile communication system according to an embodimentof the disclosure;

FIG. 2E illustrates a method of determining and applying a new MCS tablethrough an RRC signaling method before or after entry into anRRC-connected mode according to an embodiment of the disclosure;

FIG. 2F illustrates an operation in which a UE in an RRC-connected modeapplies an MCS table according to an embodiment of the disclosure;

FIG. 2G illustrates a configuration of a UE according to an embodimentof the disclosure; and

FIG. 2H illustrates a configuration of a BS according to an embodimentof the disclosure.

DETAILED DESCRIPTION

Hereinafter, the operation principle of the disclosure will be describedin detail in conjunction with the accompanying drawings. In thefollowing description of the disclosure, a detailed description of knownfunctions or configurations incorporated herein will be omitted when itmay make the subject matter of the disclosure rather unclear. The termswhich will be described below are terms defined in consideration of thefunctions in the disclosure, and may be different according to users,intentions of the users, or customs. Therefore, the definitions of theterms should be made based on the contents throughout the specification.

In the following description of the disclosure, a detailed descriptionof known relevant functions or configurations will be omitted when itmay make the subject matter of the disclosure unnecessarily unclear.Hereinafter, embodiments of the disclosure will be described withreference to the accompanying drawings.

In the following description, terms for identifying access nodes, termsreferring to network entities, terms referring to messages, termsreferring to interfaces between network entities, terms referring tovarious identification information, and the like are illustratively usedfor the sake of convenience. Therefore, the disclosure is not limited bythe terms as used below, and other terms referring to subjects havingequivalent technical meanings may be used.

In the following description, the disclosure will be described usingterms and names defined in the 3rd generation partnership project longterm evolution (3GPP LTE) standards for the convenience of description.However, the disclosure is not limited by these terms and names, and maybe applied in the same way to systems that conform other standards. Inthe disclosure, the term “eNB” may be interchangeably used with the term“gNB” for the convenience of description. That is, a base stationdescribed as “eNB” may indicate “gNB”. Further, the term “terminal” mayindicate mobile phones, NB-IoT devices, or sensors, and may alsoindicate other wireless communication devices.

First Embodiment

FIG. 1A illustrates a structure of an LTE system according to anembodiment of the disclosure.

Referring to FIG. 1A, a radio access network of the LTE system includesnext-generation base stations (hereinafter, referred to as evolved nodeBs (ENBs), Node Bs, or base stations) 1 a-05, 1 a-10, 1 a-15, and 1a-20, a mobility management entity (MME) 1 a-25, and a serving gateway(S-GW) 1 a-30. A user terminal (hereinafter, referred to as a userequipment (UE) or a terminal) 1 a-35 accesses an external networkthrough the ENBs 1 a-05 to 1 a-20 and the S-GW 1 a-30.

In FIG. 1A, the ENBs 1 a-05, 1 a-10, 1 a-15, and 1 a-20 correspond tothe existing node Bs of the UMTS system. The ENBs 1 a-05, 1 a-10, 1a-15, and 1 a-20 are connected to the UE 1 a-35 through a radio channel,and perform a more complicated role than the conventional node B. In theLTE system, since all user traffic including areal time service such asa VoIP (Voice over IP) through an Internet protocol are serviced througha shared channel, an apparatus for collecting and scheduling statusinformation on buffer statuses of UEs, available transmission powerstatus, and channel statuses is required, and the ENBs 1 a-05, 1 a-10, 1a-15, and 1 a-20 serve as this apparatus. One ENB generally controls aplurality of cells. For, example, in order to implement a transmissionrate of 100 Mbps, the LTE system uses an Orthogonal Frequency DivisionMultiplexing (OFDM) as a wireless access technology in a bandwidth of 20MHz. Further, an adaptive modulation and coding (AMC) scheme ofdetermining a modulation scheme and a channel coding rate is applieddepending on the channel status of the UE. The S-GW 1 a-30 is a devicefor providing a data bearer, and generates or removes the data bearerunder the control of the MME 1 a-25. The MME 1 a-25 is a device thatserves to perform not only a function of managing mobility of the UE 1a-35 but also various control functions and is connected to theplurality of ENBs 1 a-05, 1 a-10, 1 a-15, and 1 a-20.

FIG. 1B illustrates a structure of a wireless protocol in the LTE systemaccording to an embodiment of the disclosure.

Referring to FIG. 1B, the UE and the ENB include packet data convergenceprotocols (PDCPs) 1 b-05 and 1 b-40, radio link controls (RLCs) 1 b-10and 1 b-35, and medium access controls (MACs) 1 b-15 and 1 b-30,respectively, in the wireless protocol of the LTE system. The packetdata convergence protocols (PDCPs) 1 b-05 and 1 b-40 perform anoperation of compressing/reconstructing an IP header. Main functions ofthe PDCP are described below.

-   -   Header compression and decompression function ((Header        compression and decompression: ROHC only)    -   User data transmission function (Transfer of user data)    -   Sequential delivery function (In-sequence delivery of upper        layer PDUs at PDCP re-establishment procedure for RLC AM)    -   Reordering function (For split bearers in DC (only support for        RLC AM): PDCP PDU routing for transmission and PDCP PDU        reordering for reception)    -   Duplicate detection function (Duplicate detection of lower layer        SDUs at PDCP re-establishment procedure for RLC AM)    -   Retransmission function (Retransmission of PDCP SDUs at handover        and, for split bearers in DC, of PDCP PDUs at PDCP data-recovery        procedure, for RLC AM)    -   Ciphering and deciphering function (Ciphering and deciphering)    -   Timer-based SDU removal function (Timer-based SDU discard in        uplink)

Radio link control (RLC) 1 b-10 and 1 b-35 reconfigure the PDCP packetdata unit (PDU) to be the proper size and perform an automatic repeatrequest (ARQ) operation. Main functions of the RLC are described below.

-   -   Data transmission function (Transfer of upper layer PDUs)    -   ARQ function (Error Correction through ARQ (only for AM data        transfer))    -   Concatenation, segmentation, and reassembly function        (Concatenation, segmentation, and reassembly of RLC SDUs (only        for UM and AM data transfer))    -   Re-segmentation function (Re-segmentation of RLC data PDUs (only        for AM data transfer))    -   Reordering function (Reordering of RLC data PDUs (only for UM        and AM data transfer)    -   Duplication detection function (only for UM and AM data        transfer))    -   Error detection function (Protocol error detection (only for AM        data transfer))    -   RLC SDU deletion function (RLC SDU discard (only for UM and AM        data transfer))    -   RLC re-establishment function (RLC re-establishment)

The MACs 1 b-15 and 1 b-30 are connected with various RLC layer devicesincluded in one entity, and perform an operation for multiplexing RLCPDUs to the MAC PDU and demultiplexing the RLC PDUs from the MAC PDU.Main functions of the MAC are described below.

-   -   Mapping function (Mapping between logical channels and transport        channels)    -   Multiplexing and demultiplexing function        (Multiplexing/demultiplexing of MAC SDUs belonging to one or        different logical channels into/from transport blocks (TB)        delivered to/from the physical layer on transport channels)    -   Scheduling information report function (Scheduling information        reporting)    -   HARQ function (Error correction through HARQ)    -   Logical channel priority control function (Priority handling        between logical channels of one UE)    -   UE priority control function (Priority handling between UEs by        means of dynamic scheduling)    -   MBMS service identification function (MBMS service        identification)    -   Transport format selection function (Transport format selection)    -   Padding function (Padding)

The PHY layers 1 b-20 and 1 b-25 perform an operation for channel-codingand modulating higher-layer data to generate an OFDM symbol andtransmitting the OFDM symbol through a radio channel or demodulating andchannel-decoding the OFDM symbol received through the radio channel andtransmitting the demodulated and channel-decoded OFDM symbol to thehigher layer.

FIG. 1C illustrates a structure of a next-generation mobilecommunication system according to an embodiment of the disclosure.

Referring to FIG. 1C, a radio access network of a next-generation mobilecommunication system (hereinafter, NR or 2 g) includes a next-generationbase station 1 c-10 (new-radio node B) (hereinafter, referred to as anNR gNB or an NR base station) and a new-radio core network (NR CN) 1c-05. A user terminal 1 c-15 (hereinafter, referred to as a new radiouser equipment (NR UE) or a terminal) accesses an external networkthrough the NR gNB 1 c-10 and the NR CN 1 c-05.

In FIG. 1C, the NR gNB 1 c-10 corresponds to an evolved Node B (eNB) ofthe conventional LTE system. The NR gNB 1 c-10 may be connected to theNR UE 1 c-15 through a radio channel and may provide a better servicethan a conventional node B. Since all user traffic is served through ashared channel in the next-generation mobile communication system, adevice for collecting and scheduling status information of bufferstatuses, available transmission power statuses, and channel statuses ofUEs is required, which corresponds to the NR gNB 1 c-10. One NR gNBgenerally controls a plurality of cells. The NR gNB may have a bandwidthwider than the conventional maximum bandwidth in order to implementsuper-high-speed data transmission compared to conventional LTE and mayapply orthogonal frequency division multiplexing (OFDM) through radioaccess technology and further apply beamforming technology. Further, anadaptive modulation and coding (AMC) scheme of determining a modulationscheme and a channel coding rate is applied depending on the channelstatus of the UE. The NR CN 1 c-05 performs a function of supportingmobility, configuring a bearer, and configuring a QoS. The NR CN 1 c-05is a device that serves to perform a function of managing mobility ofthe UE 1 c-15 and various control functions and is connected to aplurality of NR gNBs. Further, the next-generation mobile communicationsystem may be linked to the conventional LTE system, and the NR CN 1c-05 is connected to an MME 1 c-25 through a network interface. The MME1 c-25 is connected to the eNB 1 c-30 which is the conventional basestation.

FIG. 1D illustrates a structure of a wireless protocol of thenext-generation mobile communication system according to an embodimentof the disclosure.

Referring to FIG. 1D, the wireless protocol of the next-generationmobile communication system includes NR SDAPs 1 d-01 and 1 d-45, NRPDCPs 1 d-05 and 1 d-40, NR RLCs 1 d-10 and 1 d-35, and NR MACs 1 d-15and 1 d-30 in the UE and the NR gNB.

The main functions of the NR SDAPs 1 d-01 and 1 d-45 may include some ofthe following functions.

-   -   User data transmission function (transfer of user-plane data)    -   Function of mapping QoS flow and a data bearer for uplink and        downlink (mapping between a QoS flow and a DRB for both DL and        UL)    -   Function of marking a QoS flow ID for uplink and downlink        (marking QoS flow ID in both DL and UL packets)    -   Function of mapping reflective QoS flow to a data bearer for        uplink SDAP PDUs (reflective QoS flow to DRB mapping for the UL        SDAP PDUs)

With respect to the SDAP layer device, the UE may receive aconfiguration as to whether to use a header of the SDAP layer device ora function of the SDAP layer device for each PDCP layer device, eachbearer, or each logical channel through an RRC message. If the SDAPheader is configured, a 1-bit indicator of NAS reflective QoS of theSDAP header and a 1 bit-indicator of AS reflective QoS may indicate thatthe UE updates or reconfigures information on mapping of QoS flow and adata bearer in uplink and downlink. The SDAP header may include QoS flowID information indicating the QoS. The QoS information may be used asdata-processing-priority or scheduling information to support a seamlessservice.

The main functions of the NR PDCPs 1 d-05 and 1 d-40 may include some ofthe following functions.

-   -   Header compression and decompression function (Header        compression and decompression: ROHC only)    -   User data transmission function (Transfer of user data)    -   Sequential delivery function (In-sequence delivery of upper        layer PDUs)    -   Non-sequential delivery function (Out-of-sequence delivery of        upper layer PDUs)    -   Reordering function (PDCP PDU reordering for reception)    -   Duplicate detection function (Duplicate detection of lower layer        SDUs)    -   Retransmission function (Retransmission of PDCP SDUs)    -   Ciphering and deciphering function (Ciphering and deciphering)    -   Timer-based SDU removal function (Timer-based SDU discard in        uplink)

The reordering function of the NR PDCP device is a function ofsequentially reordering PDCP PDUs received by a lower layer on the basisof a PDCP Sequence Number (SN), and may include a function ofsequentially transferring the reordered data to a higher layer, afunction of directly transmitting the recorded data, a function ofrecording PDCP PDUs lost due to the reordering, a function of reportingstatuses of the lost PDCP PDUs to a transmitting side, and a function ofmaking a request for retransmitting the lost PDCP PDUs.

The main functions of the NR RLC 1 d-10 or 1 d-35 may include some ofthe following functions.

-   -   Data transmission function (Transfer of upper layer PDUs)    -   Sequential delivery function (In-sequence delivery of upper        layer PDUs)    -   Non-sequential delivery function (Out-of-sequence delivery of        upper layer PDUs)    -   ARQ function (Error correction through ARQ)    -   Concatenation, segmentation, and reassembly function        (Concatenation, segmentation, and reassembly of RLC SDUs)    -   Re-segmentation function (Re-segmentation of RLC data PDUs)    -   Reordering function (Reordering of RLC data PDUs)    -   Duplicate detection function (Duplicate detection)    -   Error detection function (Protocol error detection)    -   RLC SDU deletion function (RLC SDU discard)    -   RLC re-establishment function (RLC re-establishment)

The sequential delivery function (In-sequence delivery) of the NR RLCdevice is a function of sequentially transferring RLC SDUs received froma lower layer to a higher layer, and may include, when one original RLCSDU is divided into a plurality of RLC SDUs and then received, afunction of reassembling and transmitting the RLC SDUs, a function ofreordering the received RLC PDUs on the basis of an RLC Sequence Number(SN) or a PDCP SN, a function of recording RLC PDUs lost due to thereordering, a function of reporting statuses of the lost RLC PDUs to atransmitting side, a function of making a request for retransmitting thelost RLC PDUs, if there is a lost RLC SDU, a function of sequentiallytransferring only RLC SDUs preceding the lost RLC SDU to the higherlayer, if a predetermined timer expires even though there is a lost RLCSDU, a function of sequentially transferring all RLC SDUs receivedbefore the timer starts to the higher layer, or if a predetermined timerexpires even though there is a lost RLC SDU, a function of sequentiallytransferring all RLC SDUs received up to that point in time to thehigher layer. Further, the NR RLC device may process the RLC PDUssequentially in a reception order thereof (according to an arrival orderregardless of a serial number or a sequence number) and may transfer theRLC PDUs to the PDCP device regardless of the sequence thereof(out-of-sequence delivery). In the case of segments, the NR RLC devicemay receive segments which are stored in the buffer or will be receivedin the future, reconfigure the segments to be one RLC PDU, process theRLC PDU, and then transmit the same to the PDCP device. The NR RLC layermay not include a concatenation function, and the function may beperformed by the NR MAC layer, or may be replaced with a multiplexingfunction of the NR MAC layer.

The non-sequential function (Out-of-sequence delivery) of the NR RLCdevice is a function of transferring RLC SDUs received from a lowerlayer directly to a higher layer regardless of the sequence of the RLCSDUs, and may include, when one original RLC SDU is divided into aplurality of RLC SDUs and then received, a function of reassembling andtransmitting the RLC PDUs and a function of storing RLC SNs or PDCP SNsof the received RLC PDUs, reordering the RLC PDUs, and recording lostRLC PDUs.

The NR MACs 1 d-15 and 1 d-30 may be connected to a plurality of NR RLClayer devices included in one entity, and the main functions of the NRMACs may include some of the following functions.

-   -   Mapping function (Mapping between logical channels and transport        channels)    -   Multiplexing and demultiplexing function        (Multiplexing/demultiplexing of MAC SDUs)    -   Scheduling information report function (Scheduling information        reporting)    -   HARQ function (Error correction through HARQ)    -   Logical channel priority control function (Priority handling        between logical channels of one UE)    -   UE priority control function (Priority handling between UEs by        means of dynamic scheduling)    -   MBMS service identification function (MBMS service        identification)    -   Transport format selection function (Transport format selection)    -   Padding function (Padding)

The NR PHY layers 1 d-20 and 1 d-25 perform an operation forchannel-coding and modulating higher-layer data to generate an OFDMsymbol and transmitting the OFDM symbol through a radio channel ordemodulating and channel-decoding the OFDM symbol received through theradio channel and transmitting the demodulated and channel-decoded OFDMsymbol to the higher layer.

FIG. 1E illustrates a procedure in which the UE configures an RRCconnection with the gNB when configuring a connection with a network ina next-generation mobile communication system according to an embodimentof the disclosure.

Referring to FIG. 1E, when the UE transmitting and receiving data in theRRC-connected mode has no data transmission/reception for apredetermined reason or for a predetermined time, the gNB may transmitan RRCConnectionRelease message to the UE, and the UE may switch to theRRC idle mode in step 1 e-01. When the UE of which the connection is notcurrently configured (hereinafter, referred to as an idle-mode UE) hasdata to be transmitted, the UE performs an RRC connection establishmentprocess with the gNB.

The UE establishes backward transmission synchronization with the gNBthrough a random access process and transmits an RRCConnectionRequestmessage to the gNB in step 1 e-05. The RRCConnectionRequest message mayinclude a reason (establishmentCause) to establish the connection withan identifier of the UE.

The gNB transmits an RRCConnectionSetup message to allow the UE toestablish the RRC connection in step 1 e-10. The RRCConnectionSetupmessage may include at least one piece of configuration information foreach logical channel, configuration information for each bearer,configuration information of the PDCP layer device, configurationinformation of the RLC layer device, or configuration information of theMAC layer device.

When the UE performs a handover, an indicator indicating whether toretransmit pre-configured RRC messages to a target eNB or a cell may beconfigured in the RRCConnectionSetup message. For example, theretransmission of RRC messages transmitted within several seconds beforea handover indication message is received, a handover is performed, oran RRC message is received may be indicated. The indicator may indicateeach of the pre-configured RRC messages. That is, several indicators mayindicate whether to retransmit RRC messages. Alternatively, whether toperform retransmission may be indicated in the form of a bitmapindicating each RRC message.

The RRCConnectionSetup message may indicate that an indicator forperforming a PDCP data recovery procedure is included in PDPCconfiguration information. The message may indicate that an indicatorindicating whether to perform the PDCP data recovery procedure for asignaling radio bearer (SRB) or a data radio bearer (DRB) is included inbearer configuration information. The message may indicate that anindicator indicating whether to discard data left in the PDCP layerdevice for the SRB or the DRB is included in bearer configurationinformation.

The RRCConnectionSetup message may indicate that, when a PDCPreestablishment procedure is performed, an indicator indicating whetherto perform accumulated retransmission or selective retransmission for anacknowledged mode (AM) DRB is included in bearer configurationinformation.

The UE establishing the RRC connection transmits anRRCConnectionSetupComplete to the gNB in 1 e-15. TheRRCConnectionSetupComplete message may include a control message ofSERVICE REQUEST by which the UE makes a request for configuring a bearerfor a predetermined service to the access management function (AMF) orthe MME. The gNB transmits the SERVICE REQUEST message included in theRRCConnetionSetupComplete message to the AMF or the MME in step 1 e-20.The AMF or the MME may determine whether to provide the servicerequested by the UE.

When it is determined to provide the service requested by the UE on thebasis of the determination result, the AMF or the MME transmits anINITIAL CONTEXT SETUP REQUEST message to the gNB in step 1 e-25. TheINITIAL CONTEXT SETUP REQUEST message may include quality of service(QoS) information to be applied to data radio bearer (DRB) configurationand security-related information to be applied to the DRB (for example,a security key and a security algorithm).

The gNB exchanges a SecurityModeCommand message in step 1 e-30 and aSecurityModeComplete message in step 1 e-35 in order to set securitywith the UE. When security has been completely set, the gNB transmits anRRCConnectionReconfiguration message to the UE in step 1 e-40.

When the UE performs a handover, an indicator indicating whether toretransmit pre-configured RRC messages to a target BS or a cell may beconfigured in the RRCConnectionReconfiguration message. For example, theretransmission of RRC messages transmitted within several seconds beforea handover indication message is received, a handover is performed, oran RRC message is received may be indicated. The indicator may indicateeach of the pre-configured RRC messages. That is, several indicators mayindicate whether to retransmit RRC messages. Alternatively, whether toperform the retransmission may be determined in the form of a bitmapindicating each RRC message.

The RRCConnectionReconfiguration message may indicate that an indicatorfor performing a PDCP data recovery procedure is included in PDPCconfiguration information. The message may indicate that an indicatorindicating whether to perform the PDCP data recovery procedure for anSRB or a DRB is included in bearer configuration information. Themessage may indicate that an indicator indicating whether to discarddata left in the PDCP layer device for the SRB or the DRB is included inbearer configuration information.

The RRCConnectionReconfiguration message may indicate that, when a PDCPreestablishment procedure is performed, an indicator indicating whetherto perform accumulated retransmission or selective retransmission for anAM DRB is included in bearer configuration information.

The RRCConnectionReconfiguration message may include configurationinformation of the DRB for processing user data, and the UE configuresthe DRB by applying the information and transmits anRRCConnectionReconfigurationComplete message to the gNB in step 1 e-45.The gNB completely configuring the DRB with the UE may transmit anINITIAL CONTEXT SETUP COMPLETE message to the AMF or the MME andcomplete the connection in step 1 e-50.

When the process has completely finished, the UE transmits and receivesdata to and from the gNB through a core network in steps 1 e-55 and 1e-60. According to some embodiments, the data transmission processlargely includes three steps of RRC connection configuration, securityconfiguration, and DRB configuration. Further, the gNB may transmit anRRC Connection Reconfiguration message in order to provide a newconfiguration to the UE or add or change the configuration for apredetermined reason in step 1 e-65.

When the UE performs a handover, an indicator indicating whether toretransmit pre-configured RRC messages to a target BS or a cell may beconfigured in the RRCConnectionReconfiguration message. For example, theretransmission of RRC messages transmitted within several seconds beforea handover indication message is received, a handover is performed, oran RRC message is received may be indicated. The indicator may indicateeach of the pre-configured RRC messages. That is, several indicators mayindicate whether to retransmit RRC messages. Alternatively, whether toperform the retransmission may be determined in the form of a bitmapindicating each RRC message.

The RRCConnectionReconfiguration message may indicate that an indicatorfor performing a PDCP data recovery procedure is included in PDPCconfiguration information. The message may indicate that an indicatorindicating whether to perform the PDCP data recovery procedure for asignaling radio bearer (SRB) or a data radio bearer (DRB) is included inbearer configuration information. The message may indicate that anindicator indicating whether to discard data left in the DPCP layerdevice for a signaling radio bearer (SRB) or a data radio bearer (DRB)is included in bearer configuration information.

The RRCConnectionReconfiguration message may indicate that, when a PDCPreestablishment procedure is performed, an indicator indicating whetherto perform accumulated retransmission or selective retransmission for anAM DRB is included in bearer configuration information.

According to an embodiment of the disclosure, the bearer may be ameaning including an SRB and a DRB, the SRB refers to a signaling radiobearer, and the DRB refers to a data radio bearer. An UM DRB is a DRBusing an RLC layer device operating in an unacknowledged mode (UM), andan AM DRB is a DRB using the RLC layer device operating in anacknowledged mode (AM).

FIG. 1F conceptually illustrates a handover between BSs in anext-generation mobile communication system according to an embodimentof the disclosure. When a UE 1 f-05 configures a network connection witha source BS 1 f-10 and receives an RRC message indicating a handoverfrom a BS while transmitting and receiving data, the UE may perform ahandover to a cell or a BS indicated by the RRC message in 1 f-20 ofFIG. 1F. The UE 1 f-05 may configure a new network connection with atarget BS or a cell 1 f-15 and continuously transmit data in 1 f-30 ofFIG. 1F.

When PDCP layer devices for each bearer of the UE 1 f-05 exchange datawith PDCP layer devices for each bearer of the source BS 1 f-10 andperform a handover as illustrated in 1 f-20 of FIG. 1F, the PDCP layerdevices are required to exchange data with new PDCP layer devices foreach bearer of a target BS 1 f-15 as illustrated in 1 f-30 of FIG. 1F.When the connection with a new node or BS is configured in a handoverprocedure, a security key for enhancing security is needed to be newlyupdated. That is, when the data connections with different nodes areconfigured, different security keys should be used.

After determining the handover of the UE 1 f-05 to the target BS 1 f-15,the source BS 1 f-10 may indicate a transmission and reception PDCPreestablishment procedure for each bearer to the UE in order to allowthe UE 1 f-05 successfully complete the handover.

Embodiment 1-1-1 of a PDCP reestablishment procedure between atransmission PDCP layer device (transmitting PDCP entity) and areception PDCP layer device (receiving PDCP entity) proposed in anembodiment of the disclosure is described below.

The transmission PDCP layer device and the reception PDCP layer devicemay be included in PDCP layer devices of the UE. The transmission PDCPlayer device may correspond to a part that serves to performtransmission among the PDCP layer devices of the UE, and the receptionPDCP layer device may correspond to a part that serves to perform areception function among the PDCP layer devices of the UE. Accordingly,both the transmission PDCP layer device and the reception PDCP layerdevice may be named as PDCP layer devices of the UE, and may be dividedaccording to functions thereof. Such a concept may be applied to variousembodiments of the disclosure.

When a higher layer device (for example, an RRC layer device) makes arequest for the PDCP reestablishment procedure, the transmission PDCPlayer device performs the following procedure.

1. The transmission PDCP layer device initiates a header compressionprotocol and starts an unidirectional (U) mode in an initialization andrefresh (IR) state if there is no indicator indicating the continuoususe of a header compression protocol for UM DRBs and AM DRBs.

2. The transmission PDCP layer device sets window state parameters (forexample, TX_NEXT) for UM DRBs and SRBs as initial as initial values.

3. The transmission PDCP layer device discards all stored data (forexample, PDCP SDUs or PDCP PDUs) for SRBs (since the data is RRCmessages generated to be transmitted to the source BS, the data isdiscarded not to be transmitted to the target BS).

4. The transmission PDCP layer device applies a new security keyreceived from a higher layer device (for example, an RRC layer device)and an encryption algorithm.

5. The transmission PDCP layer device applies a new security keyreceived from a higher layer device (for example, an RRC layer device)and an integrity protection algorithm.

6. For UM DRBs, the transmission PDCP layer device considers data (forexample, PDCP SDUs) which has already received PDCP serial numbers buthas not yet been transmitted to a lower layer device as data receivedfrom a higher layer (for example, an SDAP layer device or a TCP/IP layerdevice) and transmits the data in an ascending order of COUNT values (orPDCP serial numbers) allocated before PDCP reestablishment. A datadiscard timer is not restarted. Specifically, a header compressionprocedure is performed for the data, an integrity procedure or anencryption procedure is performed again, and a PDCP header is configuredand transmitted to the lower layer device.

7. For AM DRBs, the transmission PDCP layer device retransmits ortransmits all of data, of which successful transmission from lowerlayers (for example, RLC layer devices) is not identified, starting fromthe first data (for example, a PDCP SDU) in an ascending order of COUNTvalues (or PDCP serial numbers) allocated before PDCP reestablishment.That is, the accumulated retransmission is performed from the first dataof which successful transmission is not identified. Specifically, thetransmission PDCP layer device performs a header compression procedurefor the data, performs an integrity procedure or an encryption procedureagain, configures a PDCP header, and transmits the same to the lowerlayer device.

When the higher layer device (for example, the RRC layer device) makes arequest for the PDCP reestablishment procedure, the reception PDCP layerdevice performs the following procedure.

1. 1. The reception PDCP layer device processes data (for example, PDCPPDUs) received due to reestablishment of lower layer devices (forexample, RLC layer devices).

2. The reception PDCP layer device discards all stored data (forexample, PDCP SDUs or PDCP PDUs) for SRBs (the data is discarded sincethe data is RRC messages received from the source BS).

3. If a rearrangement timer runs for SRBs and UM DRBs, the receptionPDPC layer device stops and resets the timer, performs a headerdecompression procedure for all stored data (for example, PDCP SDUs) forUM DRBs and transmits the data to the higher layer device.

4. If there is no indicator indicating the continuous use of a headerdecompression protocol for AM DRBs, the reception PDCP layer deviceperforms a header decompression procedure for stored data (for example,PDCP SDUs).

5. If there is no indicator indicating the continuous use of a headerdecompression protocol for UM DRBs and AM DRBs, the reception PDCP layerdevice initiates a downlink header decompression protocol and starts ina unidirectional (U) mode of a no context (NC) state.

6. The reception PDPC layer device sets window parameters (for example,RX_NEXT and RX_DELIV) for UM DRBs and SRBs as initial values.

7. The reception PDCP layer device applies a new security key receivedfrom a higher layer device (for example, an RRC layer device) and anencryption/decryption algorithm.

8. The reception PDCP layer device applies a new security key receivedfrom a higher layer device (for example, an RRC layer device) and anintegrity protection/verification algorithm.

In Embodiment 1-1-1 of the disclosure, the transmission PDCP layerdevice always performs accumulated retransmission. However, it ispossible to perform selective retransmission so as to preventunnecessary transmission and the waste of transmission resources. Theselective retransmission refers to retransmission of only data of whichsuccessful transmission (RLC ACK) from lower layer devices (for example,RLC layer devices) is not identified by the transmission PDCP layerdevice.

However, in the case of the handover illustrated in FIG. 1F, the PDCPreestablishment procedure triggered by the BS may cause data loss ifselective retransmission is always used. It is because transmission ofall data which the PDCP layer device of the source BS 1 f-10 hassuccessfully received to the PDCP layer device of the target BS 1 f-15is not mandatory. Accordingly, although the UE 1 f-05 receives a report(RLC ACK) indicating successful reception from the source BS 1 f-10, theUE 1 f-05 is required to retransmit data of which successfultransmission is identified to the target BS 1 f-15 through RLC ACK. Thatis, the UE 1 f-05 is required to perform accumulated retransmissioncorresponding to sequential retransmission of data, of which successfultransmission is not identified in the PDCP reestablishment procedure,starting from data corresponding to a first PDCP serial number.Accordingly, even though there is data, of which successful transmission(reception of RLC ACK) from the lower layer is identified, among datahaving serial numbers larger than the first PDCP serial number, of whichsuccessful transmission is not identified, the UE 1 f-05 is required toretransmit the data.

However, if the PDCP layer device of the source BS 1 f-10 transmitssuccessfully received data to all PDCP layer devices of the target BS 1f-15, the UE 1 f-05 may perform the selective retransmission methoddescribed in Embodiment 1-1-1 of the disclosure and thus preventunnecessary retransmission and the waste of transmission resources.Accordingly, it is possible to indicate whether to perform selectiveretransmission or accumulated retransmission through a newly definedindicator when the source BS 1 f-10 performs the PDCP reestablishmentprocedure for the UE 1 f-05. For example, the selective retransmissionmay be performed when the indicator exists, and the accumulatedretransmission may be performed when the indicator does not exist.Alternatively, a 1-bit indicator may be defined, and the selectiveretransmission may be performed when the 1-bit indicator is true and theaccumulated retransmission may be performed when the 1-bit indicator isfalse. Further, the indicator may be defined by an RRC message, may beindicated by PDCP configuration information, and may be transmittedwhile being inserted into a handover indication message or an RRCreconfiguration message.

Embodiment 1-1-2 of the PDCP reestablishment procedure between thetransmission PDCP layer device (transmitting PDCP entity) and thereception PDCP layer device (receiving PDCP entity) proposed by anembodiment of the disclosure in which the selective retransmission orthe accumulated retransmission is performed according to the indicatorincluded in the RRC message of the BS is described below.

When a higher layer device (for example, an RRC layer device) makes arequest for the PDCP reestablishment procedure, the transmission PDCPlayer device performs the following procedure.

1. The transmission PDPC layer device initiates a header compressionprotocol and starts an unidirectional (U) mode in an initialization andrefresh (IR) state if there is no indicator indicating the continuoususe of a header compression protocol for UM DRBs and AM DRBs.

2. The transmission PDPC layer device sets window state parameters (forexample, TX_NEXT) for UM DRBs and SRBs as initial as initial values.

3. The transmission PDPC layer device discards all stored data (forexample, PDCP SDUs or PDCP PDUs) for SRBs (since the data is RRCmessages generated to be transmitted to the source BS, the data isdiscarded not to be transmitted to the target BS).

4. The transmission PDPC layer device applies a new security keyreceived from a higher layer device (for example, an RRC layer device)and an encryption algorithm.

5. Apply a new security key received from a higher layer device (forexample, an RRC layer device) and an integrity protection algorithm.

6. For UM DRBs, the transmission PDPC layer device considers data (forexample, PDCP SDUs) which has already received PDCP serial numbers buthas not yet been transmitted to a lower layer device as data receivedfrom a higher layer (for example, an SDAP layer device or a TCP/IP layerdevice) and transmits the data in an ascending order of COUNT values (orPDCP serial numbers) allocated before PDCP reestablishment. A datadiscard timer is not restarted. Specifically, the transmission PDPClayer device performs a header compression procedure for the data,performs an integrity procedure or an encryption procedure again,configures a PDCP header, and transmits the same to the lower layerdevice.

7. If an indicator indicating accumulated retransmission for AM DRBs isconfigured by an RRC message,

A. The transmission PDCP layer device retransmits or transmits all ofdata, of which successful transmission from lower devices (for example,RLC layer devices) is not identified, starting from the first data (forexample, a PDCP SDU) in an ascending order of COUNT values (or PDCPserial numbers) allocated before PDCP reestablishment. That is, theaccumulated retransmission is performed from the first data of whichsuccessful transmission is not identified. Specifically, a headercompression procedure is performed for the data, an integrity procedureor an encryption procedure is performed again, and a PDCP header isconfigured and transmitted to the lower layer device.

8. If an indicator indicating selective retransmission for AM DRBs isconfigured by an RRC message,

A. The transmission PDCP layer device retransmits or transmits onlydata, of which successful transmission from lower devices (for example,RLC layer devices) is not identified in an ascending order of COUNTvalues (or PDCP serial numbers) allocated before PDCP reestablishment.That is, the selective retransmission is performed only for data ofwhich successful transmission is not identified. Specifically, a headercompression procedure is performed for the data, an integrity procedureor an encryption procedure is performed again, and a PDCP header isconfigured and transmitted to the lower layer device.

When the higher layer device (for example, the RRC layer device) makes arequest for the PDCP reestablishment procedure, the reception PDCP layerdevice performs the following procedure.

1. 1. The reception PDCP layer device processes data (for example, PDCPPDUs) received due to reestablishment of lower layer devices (forexample, RLC layer devices).

2. The reception PDCP layer device discards all stored data (forexample, PDCP SDUs or PDCP PDUs) for SRBs (the data is discarded sincethe data is RRC messages received from the source BS).

3. If a rearrangement timer runs for SRBs and UM DRBs, the receptionPDPC layer device stops and resets the timer, performs a headerdecompression procedure for all stored data (for example, PDCP SDUs) forUM DRBs and transmits the data to the higher layer device.

4. If there is no indicator indicating the continuous use of a headerdecompression protocol for AM DRBs, the reception PDCP layer deviceperforms a header decompression procedure for stored data (for example,PDCP SDUs).

5. If there is no indicator indicating the continuous use of a headerdecompression protocol for UM DRBs and AM DRBs, the reception PDCP layerdevice initiates a downlink header decompression protocol and starts ina unidirectional (U) mode of a no context (NC) state.

6. The reception PDPC layer device sets window parameters (for example,RX_NEXT and RX_DELIV) for UM DRBs and SRBs as initial values.

7. The reception PDCP layer device applies a new security key receivedfrom a higher layer device (for example, an RRC layer device) and anencryption/decryption algorithm.

8. Apply a new security key received from a higher layer device (forexample, an RRC layer device) and an integrity protection/verificationalgorithm.

FIG. 1G conceptually illustrates a procedure of changing or releasingone BS of a split bearer or one radio access technology for a UE usingthe split bearer through two BSs or two radio access technologies in anext-generation mobile communication system according to an embodimentof the disclosure.

In FIG. 1G, a UE 1 g-05 may transmit and receive data through a splitbearer using two BSs (master cell groups (MCGs) 1 g-10 and secondarycell group (SCG) 1 g-15) or two radio access technologies (licensed bandand unlicensed band) as indicated by reference numeral 1 g-30.

In the split bearer, the BS may release one BS or one unlicensed band(for example, release a BS 1 g-15 as indicated by reference numeral 1g-40) or change to another BS 1 g-20 or another unlicensed band (forexample, change the BS 1 g-15 to the BS 1 g-20 as indicated by referencenumeral 1 g-50) as necessary.

In the procedure, the UE 1 g-05 may release or change the connection fordata transmission and reception through one BS or one unlicensed in thesplit bearer. In this case, the data transmitted and received throughthe connection may be lost. Accordingly, in the above case, the BS 1g-10 may instruct the UE 1 g-05 to perform a PDCP data recoveryprocedure for the split bearer.

Embodiment 1-2 for detailed description of the PDCP data recoveryprocedure of the bearer of the UE will be described below.

1. If a higher layer device (for example, an RRC layer device) makes arequest for a PDCP data recovery procedure for AM DRBs, a transmissionPDCP layer device performs the following procedure.

A. The transmission PDCP layer device retransmits only all of data ofwhich successful transmission (RLC ACK) from lower layer devices (forexample, RLC layer devices) is not identified among data (for example,PDCP PDUs) previously transmitted to a reestablished AM mode RLC layerdevice or a disconnected AM mode RLC layer device in an ascending orderof COUNT values (or PDCP serial numbers).

FIG. 1H illustrates a structure of a BS which may be implemented in anext-generation mobile communication system according to an embodimentof the disclosure.

In FIG. 1H, a very wide area may be served by one BS (5G node) in thenext-generation mobile communication system as indicated by referencenumeral 1 h-05. Specifically, there may be a CU-DU split structurewhich, referring to reference numeral 1 h-40 and reference numeral 1h-50, may be implemented by a central unit (CU) in which higher layerdevices (for example, a TCP/IP layer device, an SDAP layer device, or aPDCP layer device) 1 h-10 operate as indicated by reference numeral 1h-10 and a plurality of distributed units (DUs) 1 h-15, 1 h-30, . . . inwhich lower layer devices (for example, an RLC layer device, a MAC layerdevice, or a PHY layer device) operate as indicated by reference numeral1 h-15 and reference numeral 1 h-30 in the protocol structure. One CU 1h-10 and a plurality of DUs 1 h-15, 1 h-30, . . . may be wiredly orwirelessly connected.

A UE 1 h-20 may establish a connection to one DU 1 h-15 and transmit andreceive data in a large cell served by a BS having the above structureas indicated by reference numeral 1 h-40. As indicated by referencenumeral 1 h-50, a handover to another DU 1 h-30 within the BS may beperformed due to movement of the UE. It should be noted that thehandover within one BS in the above-described CU-DU split structure isperformed within an area served by the CU 1 h-10 without any change inthe CU 1 h-10 (that is, the same CU 1 h-10), and thus a PDCP layerdevice of the UE 1 h-20 transmitting and receiving data for each bearerand PDCP layer devices of the BS are not changed. That is, unlike thehandover illustrated in FIG. 1F, since the PDCP layer device of the BSis not changed and the handover is performed in the same node, asecurity key is not needed to be updated. Accordingly, the BS mayinstruct the UE 1 h-20 to perform a handover without any update of thesecurity key. It is because, if the security key is not updated, PDCPlayer devices of each bearer do not need to update an encryption anddecryption algorithm and an integrity protection and verificationalgorithm through a new security key and stored data is not need to beprocessed again, so that a transmission delay may be reduced.

However, data loss may be caused while the UE performs the handover, andthus a PDCP data recovery procedure is required.

Hereinafter, the disclosure proposes a PDCP data recovery procedureperformed by the UE when the BS instructs the UE to perform the handoverwithout any update of the security key.

Embodiment 1-3-1 of the PDCP data recovery procedure proposed by thedisclosure is described below. In Embodiment 1-3-1, the data recoveryprocedure is performed for SRBs, and an indicator indicating continuousmaintenance of a robust header compression (ROHC) protocol isconsidered.

When a higher layer device (for example, an RRC layer device) makes arequest for a PDCP data recovery procedure, a transmission PDCP layerdevice may perform one or a plurality of operations among the followingprocedures.

1. The transmission PDPC layer device initiates a header compressionprotocol and start an unidirectional (U) mode in an initialization andrefresh (IR) state if there is no indicator indicating the continuoususe of a header compression protocol for UM DRBs and AM DRBs.

2. The transmission PDPC layer device sets window state parameters (forexample, TX_NEXT) for UM DRBs and SRBs as initial as initial values.

3. For UM DRBs, the transmission PDPC layer device transmits data in anascending order of COUNT values (or PDCP serial numbers) for data (forexample, PDCP SDUs) which has PDCP serial numbers allocated thereto butwhich has not yet been transmitted to a lower layer device. A datadiscard timer is not restarted. If there is no indication indicating thecontinuous use of the header compression protocol, the transmission PDPClayer device performs again the header compression procedure for thedata, performs again the integrity procedure or encryption procedure,configures a PDCP header, and transmits the same to a lower layerdevice.

4. For AM DRBs, the transmission PDPC layer device retransmits ortransmits only data (for example, PDCP SUD) of which successfultransmission from lower layers (for example, RLC layer devices) is notidentified among data (for example, PDCP PDUs) which has been previouslytransmitted to a reestablished AM mode RLC layer device or adisconnected AM mode RLC layer device in an ascending order of COUNTvalues (or PDCP serial numbers). That is, the selective retransmissionis performed only for data of which successful transmission is notidentified. If there is no indication indicating the continuous use ofthe header compression protocol, the transmission PDCP layer deviceperforms the header compression procedure for the data again, performsthe integrity procedure or the encryption procedure again, configures aPDCP header, and transmits the same to a lower layer device.

5. For SRBs, the transmission PDPC layer device retransmits or transmitsonly data (for example, PDCP SDU) of which successful transmission fromlower layers (for example, RLC layer devices) is not identified amongdata (for example, PDCP PDUs) which has been previously transmitted to areestablished AM mode RLC layer device or a disconnected AM mode RLClayer device in an ascending order of COUNT values (or PDCP serialnumbers). That is, the selective retransmission is performed only fordata of which successful transmission is not identified (since the datais data configured for the same BS or CU, retransmission is performed).

When a higher layer device (for example, an RRC layer device) makes arequest for a PDCP data recovery procedure, a reception PDCP layerdevice may perform one or a plurality of operations among the followingprocedures.

1. The reception PDCP layer device processes data (for example, PDCPPDUs) received due to reestablishment of lower layer devices (forexample, RLC layer devices).

2. For SRBs, the reception PDCP layer device processes and receives allstored data (for example, PDCP SDUs or PDCP PDUs) (since the data is RRCmessages received from the same BS or CU, the data is processed andreceived).

3. If a rearrangement timer runs for SRBs and UM DRBs, the receptionPDPC layer device stops and resets the timer, performs a headerdecompression procedure for all stored data (for example, PDCP SDUs) forUM DRBs and transmits the data to the higher layer device.

4. If there is no indicator indicating the continuous use of a headerdecompression protocol for AM DRBs, the reception PDCP layer deviceperforms a header decompression procedure for stored data (for example,PDCP SDUs).

5. If there is no indicator indicating the continuous use of a headerdecompression protocol for UM DRBs and AM DRBs, the reception PDCP layerdevice initiates a downlink header decompression protocol and starts ina unidirectional (U) mode of a no context (NC) state.

6. The reception PDPC layer device sets window parameters (for example,RX_NEXT and RX_DELIV) for UM DRBs and SRBs as initial values.

Embodiment 1-3-2 of the PDCP data recovery procedure according to anembodiment of the disclosure is described below. In Embodiment 1-3-2,the data recovery procedure is performed for SRBs, and an indicatorindicating the continuous maintenance of the ROHC protocol is notconsidered.

When a higher layer device (for example, an RRC layer device) makes arequest for a PDCP data recovery procedure, a transmission PDCP layerdevice may perform one or a plurality of operations among the followingprocedures.

1. For UM DRBs, the transmission PDCP layer device transmits data in anascending order of COUNT values (or PDCP serial numbers) for data (forexample, PDCP SDUs) which has PDCP serial numbers allocated thereto buthas not yet been transmitted to a lower layer device. A data discardtimer is not restarted.

2. For AM DRBs, the transmission PDPC layer device retransmits ortransmits only data (for example, PDCP SDU) of which successfultransmission from lower layers (for example, RLC layer devices) is notidentified among data (for example, PDCP PDUs) which has been previouslytransmitted to a reestablished AM mode RLC layer device or adisconnected AM mode RLC layer device in an ascending order of COUNTvalues (or PDCP serial numbers). That is, the selective retransmissionis performed only for data of which successful transmission is notidentified.

3. For SRBs, the transmission PDPC layer device retransmits or transmitsonly data (for example, PDCP SDU) of which successful transmission fromlower layers (for example, RLC layer devices) is not identified amongdata (for example, PDCP PDUs) which has been previously transmitted to areestablished AM mode RLC layer device or a disconnected AM mode RLClayer device in an ascending order of COUNT values (or PDCP serialnumbers). That is, the selective retransmission is performed only fordata of which successful transmission is not identified (since the datais data configured for the same BS or CU, retransmission is performed).

When a higher layer device (for example, an RRC layer device) makes arequest for a PDCP data recovery procedure, a reception PDCP layerdevice may perform one or a plurality of operations among the followingprocedures.

1. 1. The reception PDCP layer device processes data (for example, PDCPPDUs) received due to reestablishment of lower layer devices (forexample, RLC layer devices).

2. For SRBs, the reception PDCP layer device processes and receives allstored data (for example, PDCP SDUs or PDCP PDUs) (since the data is RRCmessages received from the same BS or CU, the data is processed andreceived).

3. If a rearrangement timer runs for SRBs and UM DRBs, the receptionPDPC layer device stops and resets the timer, performs a headerdecompression procedure for all stored data (for example, PDCP SDUs) forUM DRBs and transmits the data to the higher layer device.

Embodiment 1-3-3 of the PDCP data recovery procedure according to anembodiment of the disclosure is described below. In Embodiment 1-3-3,the data recovery procedure is not performed for SRBs.

When a higher layer device (for example, an RRC layer device) makes arequest for a PDCP data recovery procedure, a transmission PDCP layerdevice may perform one or a plurality of operations among the followingprocedures.

1. The transmission PDPC layer device initiates a header compressionprotocol and starts an unidirectional (U) mode in an initialization andrefresh (IR) state if there is no indicator indicating the continuoususe of a header compression protocol for UM DRBs and AM DRBs.

2. The transmission PDCP layer device sets window state parameters (forexample, TX_NEXT) for UM DRBs and SRBs as initial as initial values.

3. The transmission PDCP layer device discards all stored data (forexample, PDCP SDUs or PDCP PDUs) for SRBs. (the lost RRC message isdiscarded to instruct the RRC layer device to perform retransmission bythe BS).

4. For UM DRBs, the transmission PDCP layer device considers data (forexample, PDCP SDUs) which has already received PDCP serial numbers buthas not yet been transmitted to a lower layer device as data receivedfrom a higher layer (for example, an SDAP layer device or a TCP/IP layerdevice) and transmits the data in an ascending order of COUNT values (orPDCP serial numbers) allocated before PDCP reestablishment. A datadiscard timer is not restarted. Specifically, the transmission PDCPlayer device performs a header compression procedure for the data,performs an integrity procedure or an encryption procedure again,configures a PDCP header, and transmits the same to the lower layerdevice.

5. For UM DRBs, the transmission PDCP layer device transmits data in anascending order of COUNT values (or PDCP serial numbers) for data (forexample, PDCP SDUs) which has PDCP serial numbers allocated thereto butwhich has not yet been transmitted to a lower layer device. A datadiscard timer is not restarted. If there is no indication indicating thecontinuous use of the header compression protocol, the transmission PDCPlayer device performs the header compression procedure for the dataagain, performs the integrity procedure or the encryption procedureagain, configures a PDCP header, and transmits the same to a lower layerdevice.

6. For AM DRBs, the transmission PDPC layer device retransmits ortransmits only data (for example, PDCP SDU) of which successfultransmission from lower layers (for example, RLC layer devices) is notidentified among data (for example, PDCP PDUs) which has been previouslytransmitted to a reestablished AM mode RLC layer device or adisconnected AM mode RLC layer device in an ascending order of COUNTvalues (or PDCP serial numbers). That is, the selective retransmissionis performed only for data of which successful transmission is notidentified. If there is no indication indicating the continuous use ofthe header compression protocol, the transmission PDCP layer deviceperforms the header compression procedure for the data again, performsthe integrity procedure or the encryption procedure again, configures aPDCP header, and transmits the same to a lower layer device.

When a higher layer device (for example, an RRC layer device) makes arequest for a PDCP data recovery procedure, a reception PDCP layerdevice may perform one or a plurality of operations among the followingprocedures.

1. 1. The reception PDCP layer device processes data (for example, PDCPPDUs) received due to reestablishment of lower layer devices (forexample, RLC layer devices).

2. The reception PDCP layer device discards all stored data (forexample, PDCP SDUs or PDCP PDUs) for SRBs (the data is discarded sincethe data is RRC messages received from the BS long time ago).

3. If a rearrangement timer runs for SRBs and UM DRBs, the receptionPDPC layer device stops and resets the timer, performs a headerdecompression procedure for all stored data (for example, PDCP SDUs) forUM DRBs and transmits the data to the higher layer device.

4. If there is no indicator indicating the continuous use of a headerdecompression protocol for AM DRBs, the reception PDCP layer deviceperforms a header decompression procedure for stored data (for example,PDCP SDUs).

5. If there is no indicator indicating the continuous use of a headerdecompression protocol for UM DRBs and AM DRBs, the reception PDCP layerdevice initiates a downlink header decompression protocol and starts ina unidirectional (U) mode of a no context (NC) state.

6. The reception PDPC layer device sets window parameters (for example,RX_NEXT and RX_DELIV) for UM DRBs and SRBs as initial values.

Embodiment 1-3-4 of the PDCP data recovery procedure proposed by thedisclosure is described below. In Embodiment 1-3-4, different PDCP datarecovery procedures are performed according to an indication of the BS.

The UE may receive an RRCReconfiguration message includingreconfigurationWithSync and srb-ToAddModList from the BS, and a PDCPdata recovery procedure is applied for already configured SRBs amongSRBs specified in SRB-ToAddMod of the message.

1. If SRB-ToAddMod includes an indication (reestablishPDCP) indicatingreestablishment of a PDPC layer device, Embodiment 1-1-1 or Embodiment1-1-2 of the disclosure is performed.

2. If SRB-ToAddMod includes an indication (recoverPDCP) indicatingrecovery of a PDPC layer device, Embodiment 1-3-1 or Embodiment 1-3-2 ofthe disclosure is performed.

3. If SRB-ToAddMod includes an indication (discardOnPDCP) indicatingdiscard of data of a PDCP layer device, Embodiment 1-3-3 of thedisclosure is performed.

When the procedure is completed, an RRCReconfigurationComplete messageis transmitted to the BS.

In Embodiment 1-3-1, Embodiment 1-3-2, or Embodiment 1-3-3 of the PDCPdata recovery procedure of the disclosure, the procedure for SRBs may beperformed by the BS only when the BS transmits an indication through anewly defined indicator in an RRC message.

Hereinafter, the disclosure proposes a procedure in which an RRC layerdevice of the UE retransmits an RRC message when the BS instructs the UEto perform a handover with an update of a security key or a handoverwithout any update of a security key. When the UE performs a handover,RRC messages transmitted before a handover command are notretransmitted, and thus the RRC messages may be lost. Accordingly, theBS does not successfully receive RRC messages from the UE, the BS maytransmits an RRC message including an indicator indicatingretransmission of specific RRC messages so as to make a request forretransmitting the specific RRC messages to the UE.

Embodiment 1-4-1 in which the BS makes a request for retransmitting anRRC message to the UE according to an embodiment of the disclosure isdescribed below. In Embodiment 1-4-1, the BS makes a request forretransmitting specific RRC messages to an RRC layer device of the UEthrough one indicator.

1. The BS and the UE may define specific RRC message types which can beretransmitted. The specific RRC messages may be RRC messages whichshould be transmitted when a specific function is configured in the UE.For example, in the case of a UE in which power preference indications,UE overheating assistance information, SPS assistance information, adelay budget report, and maximum bandwidth preference indications areconfigured, RRC messages which should be transmitted according to theconfiguration may be defined as specific RRC messages which should beretransmitted.

2. The BS may transmit an RRC message to the UE and define a newindicator to make a request for retransmit specific RRC messages.

3. When the indicator making a request for retransmitting specific RRCmessages is included in RRC messages received from the BS, an RRC layerdevice of the UE may retransmit all of the defined specific RRC messageswhich can be retransmitted. That is, the RRC messages may be transmittedto a lower layer device (for example, a PDCP layer device).

4. Time points at which the specific RRC messages are retransmitted maybe one or a plurality of the following conditions.

A. A time point at which an RRC message indicating an indicator making arequest for retransmitting a specific RRC message is received from theBS

B. A time point at which specific system information of a BS or a cellperforming a handover is received

C. When an RRC message including an indicator making a request forretransmitting a specific RRC message is received from the BS and apredetermined condition defined by the BS is satisfied, only RRCmessages transmitted within a preset time (for example, last one second)before an RRC message (for example, an RRCReconfiguration message or ahandover indication message) is received may be retransmitted. Forexample, only RRC messages transmitted during the last one second beforean RRC message including specific information is received may beretransmitted (during the last 1 second preceding reception of theRRCConnectionReconfiguration message including mobilityControlInfo).

Embodiment 1-4-2 in which the BS makes a request for retransmitting anRRC message to the UE according to an embodiment of the disclosure isdescribed below. In Embodiment 1-4-2, the BS defines and makes a requestfor a retransmission request indicator for each RRC message to make anRRC layer device of the UE retransmit specific RRC messages.

1. The BS and the UE may define specific RRC message types which can beretransmitted. The specific RRC messages may be RRC messages whichshould be transmitted when a specific function is configured in the UE.For example, in the case of a UE in which power preference indications,UE overheating assistance information, SPS assistance information, adelay budget report, and maximum bandwidth preference indications areconfigured, RRC messages which should be transmitted according to theconfiguration may be defined as specific RRC messages which should beretransmitted.

2. The BS may transmit an RRC message to the UE and define a newindicator for each RRC message to make a request for retransmittingspecific RRC messages.

3. When indicators making a request for retransmitting specific RRCmessages are included in RRC messages received from the BS, an RRC layerdevice of the UE may retransmit the defined specific RRC messages whichcan be retransmitted if the retransmission is indicated by an indicator.That is, the RRC messages may be transmitted to a lower layer device(for example, a PDCP layer device).

4. Time points at which the specific RRC messages are retransmitted maybe one or a plurality of the following conditions.

A. A time point at which an RRC message indicating an indicator making arequest for retransmitting a specific RRC message is received from theBS

B. A time point at which specific system information of a BS or a cellperforming a handover is received

C. When an RRC message including an indicator making a request forretransmitting a specific RRC message is received from the BS and apredetermined condition defined by the BS is satisfied, only RRCmessages transmitted within the last one second before an RRC message(for example, an RRCReconfiguration message or a handover indicationmessage) is received may be retransmitted. For example, only RRCmessages transmitted during the last one second before an RRC messageincluding specific information is received may be retransmitted (duringthe last 1 second preceding reception of theRRCConnectionReconfiguration message including mobilityControlInfo).

Embodiment 1-4-3 in which the BS makes a request for retransmitting anRRC message to the UE according to an embodiment of the disclosure isdescribed below. In Embodiment 1-4-3, a new retransmission requestindicator is defined and requested to make an RRC layer device of the UEretransmit all RRC messages transmitted for the last one second beforethe UE receives an RRC message including specific information.

1. The BS may transmit an RRC message to the UE and define a newindicator to make a request for retransmitting specific RRC messages.The specific RRC messages may be all RRC messages transmitted for thelast one second before the UE receives an RRC message including specificinformation.

2. When an indicator making a request for retransmitting specific RRCmessages is included in RRC messages received by the UE from the BS, anRRC layer device of the UE may retransmit the specific RRC messages.That is, the RRC messages may be transmitted to a lower layer device(for example, a PDCP layer device).

3. Time points at which the specific RRC messages are retransmitted maybe one or a plurality of the following conditions.

A. A time point at which an RRC message indicating an indicator making arequest for retransmitting a specific RRC message is received from theBS

B. A time point at which specific system information of a BS or a cellperforming a handover is received

C. When an RRC message including an indicator making a request forretransmitting a specific RRC message is received from the BS and apredetermined condition defined by the BS is satisfied, only RRCmessages transmitted within the last one second before an RRC message(for example, an RRCReconfiguration message or a handover indicationmessage) is received may be retransmitted. For example, only RRCmessages transmitted during the last one second before an RRC messageincluding specific information is received may be retransmitted (duringthe last 1 second preceding reception of theRRCConnectionReconfiguration message including mobilityControlInfo).

The PDCP data recovery procedures, the PDCP data recovery procedure forthe SRB, or the RRC message retransmission procedures for retransmissionby the RRC layer device, proposed by the disclosure, may be or may notbe supported by UE capability and thus may be defined as one function ofthe UE capability, and whether the UE supports the function, which isthe UE capability, may be reported to the BS.

Further, the UE may identify whether the procedure is supported by theBS through system information of the BS or the cell which the UEaccesses.

FIG. 1I illustrates a UE operation according to an embodiment of thedisclosure.

In FIG. 1I, when receiving RRC messages from the BS in step 1 i-05, a UE1 i-01 identifies information and indications included in the RRCmessages, determines which procedure will be performed according to theRRC messages among the proposed embodiments of the disclosure, in step 1i-10, and performs a procedure proposed by the disclosure in step 1i-15.

FIG. 1J illustrates a configuration of a UE according to an embodimentof the disclosure.

Referring to FIG. 1J, the UE includes a radio-frequency (RF) processor 1j-10, a baseband processor 1 j-20, a storage unit 1 j-30, and acontroller 1 j-40. The controller 1 j-40 may include a multi-connectionprocessor 1 j-42.

The RF processor 1 j-10 performs a function for transmitting andreceiving a signal through a radio channel, such as band conversion andamplification of a signal. That is, the RF processor 1 j-10 up-convertsa baseband signal provided from the baseband processor 1 j-20 into an RFband signal, transmits the RF band signal through an antenna, and thendown-converts the RF band signal received through the antenna into abaseband signal. For example, the RF processor 1 j-10 may include atransmission filter, a reception filter, an amplifier, a mixer, anoscillator, a digital-to-analog convertor (DAC), an analog-to-digitalconvertor (ADC), and the like. Although FIG. 2J illustrates only oneantenna, the UE may include a plurality of antennas. Further, the RFprocessor 1 j-10 may include a plurality of RF chains. In addition, theRF processor 1 j-10 may perform beamforming. For the beamforming, the RFprocessor 1 j-10 may control the phase and size of each signaltransmitted/received through a plurality of antennas or antennaelements. The RF processor may perform MIMO and receive a plurality oflayers when performing the MIMO operation. The RF processor 1 j-10 mayperform reception beam sweeping by properly configuring a pluralityantennas or antenna elements according to the control of the controlleror may adjust a direction of a reception beam and a beam width such thatthe reception beam cooperates with a transmission beam.

The baseband processor 1 j-20 performs a function for conversion betweena baseband signal and a bitstream according to a physical layer standardof the system. For example, in data transmission, the baseband processor1 j-20 generates complex symbols by encoding and modulating atransmission bitstream. Further, in data reception, the basebandprocessor 1 j-20 reconstructs a reception bitstream by demodulating anddecoding a baseband signal provided from the RF processor 1 j-10. Forexample, in an orthogonal frequency division multiplexing (OFDM) scheme,when data is transmitted, the baseband processor 1 j-20 generatescomplex symbols by encoding and modulating a transmission bitstream,mapping the complex symbols to subcarriers, and then configures OFDMsymbols through an inverse fast Fourier transform (IFFT) operation and acyclic prefix (CP) insertion. Further, when data is received, thebaseband processor 1 j-20 divides the baseband signal provided from theRF processor 1 j-10 in units of OFDM symbols, reconstructs the signalsmapped to the subcarriers through a fast Fourier transform (FFT)operation, and then reconstructs a reception bitstream throughdemodulation and decoding.

The baseband processor 1 j-20 and the RF processor 1 j-10 transmit andreceive signals as described above. Accordingly, each of the basebandprocessor 1 j-20 and the RF processor 1 j-10 may be referred to as atransmitter, a receiver, a transceiver, or a communication unit. Atleast one of the baseband processor 1 j-20 and the RF processor 1 j-10may include a plurality of communication modules to support a pluralityof different radio access technologies. At least one of the basebandprocessor 1 j-20 and the RF processor 1 j-10 may include differentcommunication modules to process signals in different frequency bands.For example, the different radio access technologies may include an LTEnetwork and an NR network. Further, the different frequency bands mayinclude a super high frequency (SHF) (for example, 2.2 gHz and 2 ghz)band and a millimeter (mm) wave (for example, 60 GHz) band.

The storage unit 1 j-30 stores data such as a basic program, anapplication, and configuration information for the operation of the UE.The storage unit 1 j-30 provides stored data according to a request fromthe controller 1 j-40.

The controller 1 j-40 controls the overall operation of the UE. Forexample, the controller 1 j-40 transmits and receives signals throughthe baseband processor 1 j-20 and the RF processor 1 j-10. Further, thecontroller 1 j-40 records data in the storage unit 1 j-30 and reads thedata. To this end, the controller 1 j-40 may include at least oneprocessor. For example, the controller 1 j-40 may include acommunications processor (CP) that performs control for communication,and an application processor (AP) that controls higher layers such as anapplication layer.

FIG. 1K illustrates a BS according to an embodiment of the disclosure.

As illustrated in FIG. 1K, the BS includes an RF processor 1 k-10, abaseband processor 1 k-20, a backhaul communication unit 1 k-30, astorage unit 1 k-40, and a controller 1 k-50. The controller 1 k-50 mayinclude a multi-connection processor 1 k-52.

The RF processor 1 k-10 performs a function for transmitting andreceiving a signal through a wireless channel, such as band conversionand amplification of a signal. That is, the RF processor 1 k-10up-converts a baseband signal provided from the baseband processor 1k-20 into an RF band signal, transmits the converted signal through anantenna, and down-converts an RF band signal received through theantenna into a baseband signal. For example, the RF processor 1 k-10 mayinclude a transmission filter, a reception filter, an amplifier, amixer, an oscillator, a DAC, and an ADC. Although FIG. 1K illustratesonly one antenna, the first access node may include a plurality ofantennas. Further, the RF processing unit 1 k-10 may include a pluralityof RF chains. In addition, the RF processor 1 k-10 may performbeamforming. For the beamforming, the RF processor 1 k-10 may controlthe phase and the size of each of the signals transmitted and receivedthrough a plurality of antennas or antenna elements. The RF processormay perform a downlink MIMO operation by transmitting one or morelayers.

The baseband processor 1 k-20 performs a function of conversion betweena baseband signal and a bitstream according to a physical-layer standardof the first radio access technology. For example, when data istransmitted, the baseband processor 1 k-20 generates complex symbols byencoding and modulating a transmission bitstream. Further, when data isreceived, the baseband processor 1 k-20 reconstructs a receptionbitstream by demodulating and decoding a baseband signal provided fromthe RF processor 1 k-10. For example, in an OFDM scheme, when data istransmitted, the baseband processor 1 k-20 may generate complex symbolsby encoding and modulating the transmission bitstream, map the complexsymbols to subcarriers, and then configure OFDM symbols through an IFFToperation and CP insertion. In addition, when data is received, thebaseband processor 1 k-20 divides a baseband signal provided from the RFprocessor 1 k-10 in units of OFDM symbols, recovers signals mapped withsubcarriers through an FFT operation, and then recovers a receptionbitstream through demodulation and decoding. The baseband processor 1k-20 and the RF processor 1 k-10 transmit and receive a signal asdescribed above. Accordingly, each of the baseband processor 1 k-20 andthe RF processor 1 k-10 may be referred to as a transmitter, a receiver,a transceiver, a communication unit, or a wireless communication unit.

The communication unit 1 k-30 provides an interface for communicatingwith other nodes within the network.

The storage unit 1 k-40 stores data such as a basic program, anapplication, and configuration information for the operation of theMeNB. Particularly, the storage unit 1 k-40 may store information on abearer allocated to the accessed UE and the result of measurementreported from the accessed UE The storage unit 1 k-40 may storeinformation which is a reference for determining whether to providemulti connections to the UE or stop the connections. The storage unit 1k-40 provides stored data in response to a request from the controller 1k-50.

The controller 1 k-50 controls the overall operation of the MeNB. Forexample, the controller 1 k-50 transmits and receives signals throughthe baseband processor 1 k-20 and the RF processor 1 k-10 or through thebackhaul communication unit 1 k-30. Further, the controller 1 k-50records data in the storage unit 1 k-40 and reads the data. To this end,the controller 1 k-50 may include at least one processor.

Second Embodiment

FIG. 2A illustrates a structure of an LTE system according to anembodiment of the disclosure.

Referring to FIG. 2A, a radio access network of the LTE system includesnext-generation base stations (evolved node Bs (ENBs), Node Bs, or basestations) 2 a-05, 2 a-10, 2 a-15, and 2 a-20, a mobility managemententity (MME) 2 a-25, and a serving gateway (S-GW) 2 a-30. A userequipment (UE or terminal) 2 a-35 accesses an external network throughthe ENBs 2 a-05, 2 a-10, 2 a-15, and 2 a-20, and the S-GW 2 a-30.

In FIG. 2A, the ENBs 2 a-05, 2 a-10, 2 a-15, and 2 a-20 correspond tothe existing node Bs of the UMTS system. The ENB 2 a-05 is connected tothe UE 2 a-35 through a radio channel, and performs a more complicatedrole than the conventional node B. In the LTE system, since all usertraffic including a real time service such as a VoIP (Voice over IP)through an Internet protocol are serviced through a shared channel, anapparatus for collecting and scheduling status information on bufferstatuses of UEs, available transmission power status, and channelstatuses is required, and the ENBs 2 a-05, 2 a-10, 2 a-15, and 2 a-20serve as this apparatus. One ENB generally controls a plurality ofcells. For, example, in order to implement a transmission rate of 100Mbps, the LTE system uses orthogonal frequency division multiplexing(OFDM) as a radio access technology in a bandwidth of 20 MHz. Further,an adaptive modulation and coding (AMC) scheme of determining amodulation scheme and a channel coding rate is applied depending on thechannel status of the UE. The S-GW 2 a-30 is a device for providing adata bearer, and generates or removes the data bearer under a control ofthe MME 2 a-25. The MME 2 a-35 is a device which serves to perform notonly a function of managing mobility of the UE 2 a-35 but also variouscontrol functions and is connected to a plurality of ENBs.

FIG. 2B illustrates a structure of a wireless protocol in the LTE systemaccording to an embodiment of the disclosure.

Referring to FIG. 2B, the UE and the ENB include packet data convergenceprotocols (PDCPs) 2 b-05 and 2 b-40, radio link controls (RLCs) 2 b-10and 2 b-35, and medium access controls (MACs) 2 b-15 and 2 b-30,respectively, in the wireless protocol of the LTE system. The packetdata convergence protocols (PDCPs) 2 b-05 and 2 b-40 performs anoperation of compressing/reconstructing an IP header. Main functions ofthe PDCP are described below.

-   -   Header compression and decompression function ((Header        compression and decompression: ROHC only)    -   User data transmission function (Transfer of user data)    -   Sequential delivery function (In-sequence delivery of upper        layer PDUs at PDCP re-establishment procedure for RLC AM)    -   Reordering function (For split bearers in DC (only support for        RLC AM): PDCP PDU routing for transmission and PDCP PDU        reordering for reception)    -   Duplicate detection function (Duplicate detection of lower layer        SDUs at PDCP re-establishment procedure for RLC AM)    -   Retransmission function (Retransmission of PDCP SDUs at handover        and, for split bearers in DC, of PDCP PDUs at PDCP data-recovery        procedure, for RLC AM)    -   Ciphering and deciphering function (Ciphering and deciphering)    -   Timer-based SDU removal function (Timer-based SDU discard in        uplink)

Radio link control (RLC) 2 b-10 and 2 b-35 reconfigure the PDCP packetdata unit (PDU) to be the proper size and perform an ARQ operation. Mainfunctions of the RLC are described below.

-   -   Data transmission function (Transfer of upper layer PDUs)    -   ARQ function (Error Correction through ARQ (only for AM data        transfer))    -   Concatenation, segmentation, and reassembly function        (Concatenation, segmentation, and reassembly of RLC SDUs (only        for UM and AM data transfer))    -   Re-segmentation function (Re-segmentation of RLC data PDUs (only        for AM data transfer))    -   Reordering function (Reordering of RLC data PDUs (only for UM        and AM data transfer)    -   Duplication detection function (only for UM and AM data        transfer))    -   Error detection function (Protocol error detection (only for AM        data transfer))    -   RLC SDU deletion function (RLC SDU discard (only for UM and AM        data transfer))    -   RLC re-establishment function (RLC re-establishment)

The MACs 2 b-15 and 2 b-30 are connected with various RLC layer devicesincluded in one entity, and perform an operation for multiplexing RLCPDUs to the MAC PDU and demultiplexing the RLC PDUs from the MAC PDU.Main functions of the MAC are described below.

-   -   Mapping function (Mapping between logical channels and transport        channels)    -   Multiplexing and demultiplexing function        (Multiplexing/demultiplexing of MAC SDUs belonging to one or        different logical channels into/from transport blocks (TB)        delivered to/from the physical layer on transport channels)    -   Scheduling information report function (Scheduling information        reporting)    -   HARQ function (Error correction through HARQ)    -   Logical channel priority control function (Priority handling        between logical channels of one UE)    -   UE priority control function (Priority handling between UEs by        means of dynamic scheduling)    -   MBMS service identification function (MBMS service        identification)    -   Transport format selection function (Transport format selection)    -   Padding function (Padding)

The PHY layers 2 b-20 and 2 b-25 perform an operation for channel-codingand modulating higher-layer data to generate an OFDM symbol andtransmitting the OFDM symbol through a radio channel or demodulating andchannel-decoding the OFDM symbol received through the radio channel andtransmitting the demodulated and channel-decoded OFDM symbol to thehigher layer.

FIG. 2C illustrates a structure of a next-generation mobilecommunication system according to an embodiment of the disclosure.

Referring to FIG. 2C, a radio access network of a next-generation mobilecommunication system (hereinafter, NR or 2 g) includes a next-generationbase station 2 c-10 (new-radio node B) (hereinafter, referred to as anNR gNB or an NR base station) and a new-radio core network (NR CN) 2c-05. A user equipment 2 c-15 (hereinafter, referred to as a new radiouser equipment (NR UE) or a terminal) accesses an external networkthrough the NR gNB 2 c-10 and the NR CN 2 c-05.

In FIG. 2C, the NR gNB 2 c-10 corresponds to an evolved Node B (eNB) ofthe conventional LTE system. The NR gNB 2 c-10 may be connected to theNR UE 2 c-15 through a radio channel and may provide better service thana conventional node B. Since all user traffic is served through a sharedchannel in the next-generation mobile communication system, a device forcollecting and scheduling status information of buffer statuses,available transmission power statuses, and channel statuses of UEs isrequired, which corresponds to the NR gNB 2 c-10. One NR gNB generallycontrols a plurality of cells. The NR gNB may have a bandwidth widerthan the conventional maximum bandwidth in order to implementsuper-high-speed data transmission compared to conventional LTE and mayapply orthogonal frequency division multiplexing (OFDM) through radioaccess technology and further apply beamforming technology. Further, anadaptive modulation and coding (AMC) scheme of determining a modulationscheme and a channel coding rate is applied depending on the channelstatus of the UE. The NR CN 2 c-05 performs a function of supportingmobility, configuring a bearer, and configuring a QoS. The NR CN 2 c-05is a device that serves to perform a function of managing mobility ofthe UE 2 c-15 and various control functions and is connected to aplurality of NR gNBs. Further, the next-generation mobile communicationsystem may be linked to the conventional LTE system, and the NR CN 2c-05 is connected to an MME 2 c-25 through a network interface. The MME2 c-25 is connected to the eNB 2 c-30 which is the conventional basestation.

FIG. 2D illustrates a structure of a wireless protocol of thenext-generation mobile communication system according to an embodimentof the disclosure.

Referring to FIG. 2D, the UE and the NR gNB include NR SDAPs 2 d-01 and2 d-45, NR PDCPs 2 d-05 and 2 d-40, NR RLCs 2 d-10 and 2 d-35, and NRMACs 2 d-15 and 2 d-30 in the wireless protocol of the next-generationmobile communication system.

The main functions of the NR SDAPs 2 d-01 and 2 d-45 may include some ofthe following functions.

-   -   User data transmission function (transfer of user-plane data)    -   Function of mapping QoS flow and a data bearer for uplink and        downlink (mapping between a QoS flow and a DRB for both DL and        UL)    -   Function of marking a QoS flow ID for uplink and downlink        (marking QoS flow ID in both DL and UL packets)    -   Function of mapping reflective QoS flow to a data bearer for        uplink SDAP PDUs (reflective QoS flow to DRB mapping for the UL        SDAP PDUs)

With respect to the SDAP layer device, the UE may receive aconfiguration as to whether to use a header of the SDAP layer device ora function of the SDAP layer device for each PDCP layer device, eachbearer, or each logical channel through an RRC message. If the SDAPheader is configured, a 1-bit indicator of NAS reflective QoS of theSDAP header and a 1 bit-indicator of AS reflective QoS may indicate thatthe UE updates or reconfigures information on mapping of QoS flow and adata bearer in uplink and downlink. The SDAP header may include QoS flowID information indicating the QoS. The QoS information may be used asdata-processing-priority or scheduling information to support a seamlessservice.

The main functions of the NR PDCPs 2 d-05 and 2 d-40 may include some ofthe following functions.

-   -   Header compression and decompression function (Header        compression and decompression: ROHC only)    -   User data transmission function (Transfer of user data)    -   Sequential delivery function (In-sequence delivery of upper        layer PDUs)    -   Non-sequential delivery function (Out-of-sequence delivery of        upper layer PDUs)    -   Reordering function (PDCP PDU reordering for reception)    -   Duplicate detection function (Duplicate detection of lower layer        SDUs)    -   Retransmission function (Retransmission of PDCP SDUs)    -   Ciphering and deciphering function (Ciphering and deciphering)    -   Timer-based SDU removal function (Timer-based SDU discard in        uplink)

The reordering function of the NR PDCP device is a function ofsequentially reordering PDCP PDUs received by a lower layer on the basisof a PDCP Sequence Number (SN), and may include a function ofsequentially transferring the reordered data to a higher layer, afunction of directly transmitting the recorded data, a function ofrecording PDCP PDUs lost due to the reordering, a function of reportingstatuses of the lost PDCP PDUs to a transmitting side, and a function ofmaking a request for retransmitting the lost PDCP PDUs.

The main functions of the NR RLC 2 d-10 and 2 d-35 may include some ofthe following functions.

-   -   Data transmission function (Transfer of upper layer PDUs)    -   Sequential delivery function (In-sequence delivery of upper        layer PDUs)    -   Non-sequential delivery function (Out-of-sequence delivery of        upper layer PDUs)    -   ARQ function (Error correction through ARQ)    -   Concatenation, segmentation, and reassembly function        (Concatenation, segmentation, and reassembly of RLC SDUs)    -   Re-segmentation function (Re-segmentation of RLC data PDUs)    -   Reordering function (Reordering of RLC data PDUs)    -   Duplicate detection function (Duplicate detection)    -   Error detection function (Protocol error detection)    -   RLC SDU deletion function (RLC SDU discard)    -   RLC re-establishment function (RLC re-establishment)

The sequential delivery function (In-sequence delivery) of the NR RLCdevice is a function of sequentially transferring PDCP SDUs receivedfrom a lower layer to a higher layer, and may include, when one originalRLC SDU is divided into a plurality of RLC SDUs and then received, afunction of reassembling and transmitting the RLC SDUs, a function ofreordering the received RLC PDUs on the basis of an RLC Sequence Number(SN) or a PDCP SN, a function of recording PDCP PDUs lost due to thereordering, a function of reporting statuses of the lost PDCP PDUs to atransmitting side, a function of making a request for retransmitting thelost PDCP PDUs, a function of, if there is a lost RLC SDU, sequentiallytransferring only RLC SDUs preceding the lost RLC SDU to the higherlayer, a function of, if a predetermined timer expires even though thereis a lost RLC SDU, sequentially transferring all RLC SDUs receivedbefore the timer starts to the higher layer, or a function of, if apredetermined timer expires even though there is a lost RLC SDU,sequentially transferring all RLC SDUs received up to that point in timeto the higher layer. Further, the NR RLC device may process the RLC PDUssequentially in a reception order thereof (according to an arrival orderregardless of a serial number or a sequence number) and may transfer theRLC PDUs to the PDCP device regardless of the sequence thereof(out-of-sequence delivery). In the case of segments, the NR RLC devicemay receive segments which are stored in the buffer or will be receivedin the future, reconfigure the segments to be one RLC PDU, process theRLC PDU, and then transmit the same to the PDCP device. The NR RLC layermay not include a concatenation function, and the function may beperformed by the NR MAC layer, or may be replaced with a multiplexingfunction of the NR MAC layer.

The non-sequential function (Out-of-sequence delivery) of the NR RLCdevice is a function of transferring RLC SDUs received from a lowerlayer directly to a higher layer regardless of the sequence of the RLCSDUs, and may include, when one original RLC SDU is divided into aplurality of RLC SDUs and then received, a function of reassembling andtransmitting the RLC PDUs and a function of storing RLC SNs or PDCP SNsof the received RLC PDUs, reordering the RLC PDUs, and recording lostRLC PDUs.

The NR MACs 2 d-15 and 2 d-30 may be connected to a plurality of NR RLClayer devices included in one entity, and the main functions of the NRMACs may include some of the following functions.

-   -   Mapping function (Mapping between logical channels and transport        channels)    -   Multiplexing and demultiplexing function        (Multiplexing/demultiplexing of MAC SDUs)    -   Scheduling information report function (Scheduling information        reporting)    -   HARQ function (Error correction through HARQ)    -   Logical channel priority control function (Priority handling        between logical channels of one UE)    -   UE priority control function (Priority handling between UEs by        means of dynamic scheduling)    -   MBMS service identification function (MBMS service        identification)    -   Transport format selection function (Transport format selection)    -   Padding function (Padding)

The NR PHY layers 2 d-20 and 2 d-25 perform an operation forchannel-coding and modulating higher-layer data to generate an OFDMsymbol and transmitting the OFDM symbol through a radio channel ordemodulating and channel-decoding the OFDM symbol received through theradio channel and transmitting the demodulated and channel-decoded OFDMsymbol to the higher layer.

In the LTE system or the next-generation mobile communication system,the UE determines a modulation and coding scheme (MCS) in order toefficiently transmit and receive data to and from the BS in anRRC-connected mode. That is, the BS may determine which MCS table isconfigured in the UE. The MCS table may be classified into and definedas a total of three types through the following tables.

1. MCS table 1: supports 64QAM MCS Index Modulation Order Target codeRate Spectral I_(MCS) Q_(m) R × [1024] efficiency 0 2 120 0.2344 1 2 1570.3066 2 2 193 0.3770 3 2 251 0.4902 4 2 308 0.6016 5 2 379 0.7402 6 2449 0.8770 7 2 526 1.0273 8 2 602 1.1758 9 2 679 1.3262 10 4 340 1.328111 4 378 1.4766 12 4 434 1.6953 13 4 490 1.9141 14 4 553 2.1602 15 4 6162.4063 16 4 658 2.5703 17 6 438 2.5664 18 6 466 2.7305 19 6 517 3.029320 6 567 3.3223 21 6 616 3.6094 22 6 666 3.9023 23 6 719 4.2129 24 6 7724.5234 25 6 822 4.8164 26 6 873 5.1152 27 6 910 5.3320 28 6 948 5.554729 2 reserved 30 4 reserved 31 6 reserved

2. MCS table 2: supports 256QAM MCS Index Modulation Order Target codeRate Spectral I_(MCS) Q_(m) R × [1024] efficiency 0 2 120 0.2344 1 2 1930.3770 2 2 308 0.6016 3 2 449 0.8770 4 2 602 1.1758 5 4 378 1.4766 6 4434 1.6953 7 4 490 1.9141 8 4 553 2.1602 9 4 616 2.4063 10 4 658 2.570311 6 466 2.7305 12 6 517 3.0293 13 6 567 3.3223 14 6 616 3.6094 15 6 6663.9023 16 6 719 4.2129 17 6 772 4.5234 18 6 822 4.8164 19 6 873 5.115220 8 682.5 5.3320 21 8 711 5.5547 22 8 754 5.8906 23 8 797 6.2266 24 8841 6.5703 25 8 885 6.9141 26 8 916.5 7.1602 27 8 948 7.4063 28 2reserved 29 4 reserved 30 6 reserved 31 8 reserved

3. MCS table 3: supports 64QAM and is newly introduced to support URLLCservice MCS Index Modulation Order Target code Rate Spectral I_(MCS)Q_(m) R × [1024] efficiency 0 2 30 0.0586 1 2 40 0.0781 2 2 50 0.0977 32 64 0.1250 4 2 78 0.1523 5 2 99 0.1934 6 2 120 0.2344 7 2 157 0.3066 82 193 0.3770 9 2 251 0.4902 10 2 308 0.6016 11 2 379 0.7402 12 2 4490.8770 13 2 526 1.0273 14 2 602 1.1758 15 4 340 1.3281 16 4 378 1.476617 4 434 1.6953 18 4 490 1.9141 19 4 553 2.1602 20 4 616 2.4063 21 6 4382.5664 22 6 466 2.7305 23 6 517 3.0293 24 6 567 3.3223 25 6 616 3.609426 6 666 3.9023 27 6 719 4.2129 28 6 772 4.5234 29 2 reserved 30 4reserved 31 6 reserved

An embodiment of the disclosure relates to a method and an apparatus forsupporting a ultra-reliable-low latency communication (URLLC) service toa UE operating in an RRC-connected mode in a next-generation mobilecommunication system and, more particularly, to a method and anapparatus in which a BS configures new UE identifier information (newradio network temporary identifier (RNTI)) in a UE supporting a URLLCservice through RRC signaling and the UE applies a new MCS table (thatis, MCS table 3) so as to transmit and receive data to and from the BS.In an embodiment of the disclosure, new UE identifier information isreferred to as an MCS-RNTI for convenience of the description. The UEidentifier information is not limited to the term “MCS-RNTI”, but may bereferred to as an MCS-C-RNTI or an RNTI related to the use of MCS table3. Hereinafter, the term “MCS-RNTI” will be used for convenience of thedescription. Further, an embodiment of the disclosure proposes methodsby which the UE transmits and receives data to and from the BS byapplying MCS table 3 when the BS does not configure the MCS-RNTI in theUE supporting the URLLC service through RRC signaling.

An embodiment of the disclosure proposes methods by which the UEmonitors an MCS-RNTI in activated serving cells (activated SCells) in aspecific bandwidth part (BWP) through RRC signaling. Further, anembodiment of the disclosure proposes methods by which the UE performsHARQ retransmission using an MCS-RNTI when the UE performs initialtransmission to the BS through a dynamic grant and methods by which theUE performs HARQ retransmission using a configured scheduling (CS)-RNTIwhen the UE performs initial transmission to the BS through a configuredgrant.

The proposed methods may be very useful for reducing processing load ofthe UE and also useful for configuring a frequency aggregationtechnology or a dual connectivity technology by the UE in an environmentin which small cells are arranged in a macro cell.

FIG. 2E illustrates a method of determining and applying a new MCS tablethrough an RRC signaling method before or after entry into anRRC-connected mode according to an embodiment of the disclosure.

In FIG. 2E, when a UE 2 e-01 transmitting/receiving data in anRRC-connected mode has no data transmission/reception for apredetermined reason or for a predetermined time, a BS (eNB or gNB) 2e-02 transmits an RRC message (for example, an RRC connection release,RRC connection suspend, or new RRC message (for example, ToInactive)) tothe UE 2 e-01, and thus the UE 2 e-01 may switch to an RRC-idle mode oran RRC-inactive mode 2 e-15 in step 2 e-10. In the RRC-idle mode or theRRC-inactive mode, the UE 2 e-01 performs cell selection or cellreselection during movement and discovers a suitable cell, and when acell, on which the UE will camp on, reads system information of the cellin step 2 e-20. That is, the UE 2 e-01 may camp on any cell in theRRC-idle mode or the RRC-inactive mode and read information on afrequency on which frequency measurement is performed, a priority of thefrequency, and timer information from system information of thecorresponding cell (for example, SIB5 in the LTE system and SIB1, SIB2,SIB3, SIB4, or SIB5 in the next-generation mobile communication system).

In the future, when data to be transmitted is generated, the UE 2 e-01in the RRC-idle mode or the RRC-inactive mode in which the connection isnot currently established performs an RRC connection establishmentprocess with the BS 2 e-02. The UE 2 e-01 establishes backwardtransmission synchronization with the BS 2 e-02 through a random accessprocess in steps 2 e-25 and 2 e-30, and transmits anRRCConnectionRequest message to the BS in step 2 e-35. The messageincludes a reason (establishmentCause) to establish the connection withan identifier of the UE. The BS 2 e-02 transmits an RRCConnectionSetupmessage to allow the UE 2 e-01 to establish the RRC connection in step 2e-40. The message includes bearer configuration information(RadioBearerConfig) and cell group configuration information(CellGroupConfig) which are RRC connection configuration information.The RRC connection is also referred to as a signaling radio bearer(SRB), and is used for transmitting and receiving an RRC message, whichis a control message, between the UE 2 e-01 and the BS 2 e-02. The UEestablishing the RRC connection (hereinafter, referred to as a connectedmode UE) transmits an RRCConnectionSetupComplete message to the BS 2e-02 in step 2 e-45.

The RRCConectionSetupComplete message includes a control messagecorresponding to a SERVICE REQUEST by which the UE 2 e-01 makes arequest for establishing a bearer for a predetermined service to the MMEor the AMF. The BS 2 e-02 transmits the SERVICE REQUEST message includedin the RRCConnectionSetupComplete message to the MME or the AMF, and theMME or the AMF determines whether to provide the service requested bythe UE 2 e-01. When it is determined to provide the service requested bythe UE 2 e-01 on the basis of the determination result, the MME or theAMF transmits an INITIAL CONTEXT SETUP REQUEST message to the BS 2 e-02.The message includes Quality of Service (QoS) information to be appliedto Data Radio Bearer (DRB) configuration and security-relatedinformation to be applied to the DRB (for example, a security key and asecurity algorithm). The BS 2 e-02 completes security configuration byexchanging a SecurityModeCommand message and a SecurityModeCompletemessage to configure security with the UE 2 e-01 in steps 2 e-50 and 2e-55.

When the security configuration is completed in steps 2 e-50 and 2 e-55,the BS 2 e-02 transmits an RRCConnectionReconfiguration message to theUE 2 e-01 in step 2 e-60. The message may include bearer configurationinformation (RadioBearerConfig), cell group configuration information(CellGroupConfig), or frequency measurement information (MeasConfig)which the UE 2 e-01 should measure. Further, the message includesconfiguration information of the DRB for processing user data, and theUE 2 e-01 configures the DRB by applying the information and transmitsan RRCConnectionReconfigurationComplete message to the BS 2 e-02 in step2 e-65.

The BS 2 e-02 completed the DRB configuration with the UE 2 e-01transmits the INITIAL CONTEXT SETUP COMPLETE message to the MME or theAMF, and the MME or the AMF receiving the same enables data transmissionbetween an S-GW or a UPF and the BS 2 e-02 through a bearerconfiguration process with the S-GW or the UPF, and thus the UE 2 e-01transmits and receives data to and from the BS 2 e-02 via the S-GW orthe UPF through the process in step 2 e-70.

The BS 2 e-02 may transmit an RRCConnection Reconfiguration message tonewly make, add, or change configuration to the UE 2 e-01 for apredetermined reason in step 2 e-75. The RRCConnectionReconfigurationmessage may include a ReconfigurationWithSync information element (IE)including parameters for synchronization reconfiguration of a targetSpCell. When the RRCConnectionReconfiguration message of step 2 e-75includes the ReconfigurationWith Sync IE, the UE 2 e-01 performs acontent and non-content-based random access procedure with the BS 2e-02. In order to allow the UE 2 e-01 to perform the non-content-basedrandom access, dedicated random access resources may be allocated to theRRCConnectionReconfiguration message of step 2 e-75. The UE 2 e-01transmits a random access preamble through a physical channel for randomaccess in order to access the BS 2 e-02 in step 2 e-80. When the BS 2e-02 receives the preamble, a random access response (RAR) messagethereof is transmitted to the UE 2 e-01 in step 2 e-85.

The RAR message of step 2 e-85 includes identifier information of thepreamble used in step 2 e-80 to contain uplink transmission timingcorrection information, uplink resource allocation information, andtemporary UE identifier information or UE identifier information. Theuplink resource allocation information is detailed information onresources to be used by the UE 2 e-01 in the future and includes thephysical location and size of resources, a modulation and coding scheme(MCS) used for transmission, and transmission power control information.When the UE 2 e-01 transmitting the preamble performs initial access,the UE 2 e-01 does not possess an identifier allocated by the BS forcommunication with the BS 2 e-02, and thus the temporary UE identifierinformation is a transmitted value to be used for the same.

Meanwhile, when the RAR message is transmitted, the BS 2 e-02 schedulesthe corresponding RAR message through a PDCCH, and the correspondingscheduling information is scrambled using a random access-radio networktemporary identifier (RA-RNTI). The RA-RNTI is mapped to physical randomaccess channel (PRACH) resources used for transmitting the message ofstep 2 e-80, and the UE 2 e-01 transmitting the preamble throughspecific PRACH resources attempts to receive a PDCCH on the basis of thecorresponding RA-RNTI and determines whether there is a correspondingRAR message. The UE 2 e-01 receiving the RAR message determines atransport block (TB) size and an MCS table through an uplink allocatedby the RAR message, and then transmits anRRCConnectionReconfigurationComplete message to the BS 2 e-02 in step 2e-90.

When the RRCConnectionReconfiguration message of step 2 e-75 does notinclude the ReconfigurationWith Sync IE, the UE 2 e-01 transmits theRRCConnectionReconfigurationComplete message to the BS 2 e-02 withoutany random access process in step 2 e-90.

The RRC message ((RRC Connection Reconfiguration of steps 2 e-60 and 2e-75) may include the following information.

1. A cell group identifier (CellGroupID) by which a cell group can beidentified since only one master cell group (MCS) may be configured, onemaster cell group and one secondary cell group (SCG) or a plurality ofSCGs may be configured

2. RLC bearer configuration information (rlc-BearerToAddModList andrlc-BearerToReleaseList)

A. RLC bearer configuration information may include aLogicalChannelConfig information element (IE) used for configuring alogical channel parameter, and the corresponding IE may includeinformation on a time at which uplink MAC SDUs can be transmitted in alogical channel (maxPUSCH-Duration: If present, UL MAC SDUs from thislogical channel can only be transmitted using uplink grants that resultin a PUSCH duration shorter than or equal to the duration indicated bythis field. Otherwise, UL MAC SDUs from this logical channel can betransmitted using an uplink grant resulting in any PUSCH duration).

3. MAC configuration information (mac-CellGroupConfig) and PHYconfiguration information (physicalCellGroupConfig) to be configured andused for each cell group (cell group specific)

A. PHY configuration information may include only a new RNTI (MCS-RNTI)used for MCS table 3.

B. PHY configuration information may include an MCS-RNTI used for MCStable 3 and a list of bandwidth part identifiers (BWP IDs) andControlResourceSet IDs, SearchSpace IDs, and SCell identifiers (SCellIndex) corresponding to the corresponding BWP IDs (MCS-RNTI & list of{BWP id(and ControlResourceSet IDs and SearchSpace IDs), SCell Index}).

C. PHY configuration information may include a CS-RNTI value fordownlink semi-persistent scheduling (SPS) or a CS-RNTI value for uplinkconfigured grant (CG).

4. SpCell configuration information (SpCellConfig) for differentlyconfiguring a parameter of the SpCell (for example, referring to a PCellin an MCG and a PSCell in an SCG) configured for each cell group

A. SpCell configuration information may include a serving cellidentifier (ServeCellIndex) for identifying the corresponding SpCell.

B. SpCell configuration information may include aReconfigurationWithSync information element (IE) including parametersfor the synchronous reconfiguration to the target SpCell, and thecorresponding IE may include UE identifier information (for example, aC-RNTI value) and information on a target SpCell or a target Scell (forexample, a physical cell identifier (Phycell ID)).

C. Since the SpCell configuration information may introduce and use aseparate configuration parameter for each SpCell, thespCellConfigDedicated IE may include ServingCellConfig, and when thespCellConfigDedicated IE includes ServingCellConfig, configure an SpCellaccording to an indication of the configured information.

5. scellToAddModList or sCellToReleaseList information for adding,modifying, or releasing one or a plurality of SCells for each cell group

A. sCellToAddModList includes a serving cell identifier (SCellIndex) foridentifying an SCell.

B. sCellToAddModList may include common configuration parameters(ServingCellConfigCommon) for configuring several Scells at once.

C. sCellToAddModList may include configuration parameters(ServingCellConfig) for respective Scells.

D. sCellToReleaseList may include serving cell identifiers (SCellIndex)for configured SCells and, when the serving cell identifier is included,may mean release of the corresponding SCell.

6. When SCells are configured, information for configuring an initialstate as an activated state, a dormant state, or a deactivated state maybe included. When the state of each SCell is configured as an activatedstate or a dormant state through the RRC message, an integer indicatingwhen PDCCH monitoring starts may be included and configured.

7. When an initial state of each Scell is configured as an activatedstate, one or a plurality of BWPs may be configured in the SCellconfigured as the activated state and configuration information for amaximum of four BWPs may be included.

A. BWP configuration information may include frequency/time resourceinformation and subcarrier spacing information, and further includeinformation on cyclic prefix (CP) (for example, normal CP or extendedCP).

B. BWP configuration information includes uplink BWP configurationinformation. A bandwidth part identifier (BWP ID) is stated in theuplink BWP configuration information, and common configurationparameters (BWP-UplinkCommon) may be included to configure a pluralityBWP IDs at once. The common configuration parameters may include RACHconfiguration information (rach-ConfigCommon), PUSCH configurationinformation (pusch-configcommon), or PUCCH configuration information(PUCCH-ConfigCommon). Individual configuration parameters(BWP-UplinkDedicated) may be included to separately configure respectiveBWP IDs. The individual configuration parameters may include PUCCHconfiguration information (PUCCH-Config), PUSCH configurationinformation (PUSCH-Config), or ConfiguredGrantConfig.

i. A ConfiguredGrantConfig information element (IE) may include a valuewhich may indicate MCS table 3 in an mcs-Table. For example, inmcs-Table ENUMERATE {qam256, spare1}, the value indicating MCS table 3may be added to spare1. When a value of qam64 is allocated to spare1,the value may instruct the UE to apply MCS table 3. The spare fieldvalue may be configured as qam64LowSE. The configured value may be avalue indicating MCS table 3. Further, the corresponding IE may containconfiguration information for configured grant transmission(rrc-ConfiguredUplinkGrant). The UE may be instructed to transmit a ULgrant (type 2) in which DCI is a CS-RNTI when there is norrc-ConfiguredUplinkGrant field value, and the UE may be instructed totransmit a UL grant (type 1) configured as RRC when there is anrrc-ConfiguredUplinkGrant field value. Further, information(periodicity) for determining a period on which a CG is periodicallytransmitted regardless of a UL Configured Grant (CG) Type to the UE maybe included in the ConfiguredConfig IE.

ii. The PUSCH-Config IE may include information for configuring PUSCHparameters which can be applied to a specific BWP for each UE. A valueindicating MCS table 3 may be included in an mcs-Table which can beincluded in the IE. For example, in mcs-Table ENUMERATE {qam256,spare1}, the value indicating MCS table 3 may be added to spare1. When avalue of qam64 is allocated to spare1, the value may instruct the UE toapply MCS table 3.

C. BWP configuration information includes downlink BWP configurationinformation. A bandwidth part (BWP ID) is stated in the downlink BWPconfiguration information, and the downlink BWP configurationinformation may include common configuration parameters(BWP-DownlinkCommon) in order to configure a plurality of BWP IDs atonce. The common configuration parameters may include PDCCHconfiguration information (PDCCH-ConfigCommon) or PDSCH configurationinformation (PDSCH-ConfigCommon). Individual configuration parameters(BWP-DownlinkDedicated) may be included to separately configurerespective BWP IDs. The individual configuration parameters may includePDCCH configuration information (PDCCH-Config), PDSCH configurationinformation (PDSCH-Config), or SPS configuration information(SPS-Config).

i. A PDCCH-ConfigCommon information element (IE) may include informationrequired when a handover is generated, a cell for each cell group isadded/changed/or released, or a PDCCH parameter for each cell providedfrom system information (for example, SIB1) is configured.

1. The information may include one or a plurality of time/frequencycontrol resource sets (CORESETs) to find downlink control information(DCI).

2. The information may include SearchSpace defined to find a place inwhich a PDCCH is generated (SearchSpace defines how/where to search forPDCCH candidates). For example, the information may include a commonSearchSpace (commonSearchSpace) for each cell, a SearchSpace ID for anSIB1 message (searchSpaceSIB1), a SearchSpace ID for messages other thanSIB1 (searchSpaceOtherSystemInformation), a SearchSpace ID for paging(pagingSearchSpace), and a SearchSpace ID for a random access procedure(ra-SearchSpace).

ii. The PDCCH-Config IE may include information required when a PDCCHparameter for each UE is configured.

1. A list for adding or modifying a CORESET(controlResourceSetToAddModList)

2. A list for releasing a CORESET (controlResourceSetToReleaseList)

3. A list for adding or modifying a search space(searchSpaceToAddModList)

4. A list for releasing a search space (searchSpaceToReleaseList)

5. A common search space (common SearchSpace) according to a search typeand a search space for each UE (ue-specific Searchspace)

iii. A maximum of three CORESETs may be included for each BWP, and amaximum of ten search spaces may be defined and included for each BWP.Further, one search space includes information such that the searchspace is associated with one CORESET (Each search space is associatedwith one CORESET).

iv. The PDSCH-Config IE may include information for configuring a PDSCHparameter for each UE.

1. A value indicating MCS table 3 may be included in the mcs-Table. Forexample, in mcs-Table ENUMERATE {qam256, spare1}, the value indicatingMCS table 3 may be added to spare1. When a value of qam64 is allocatedto spare1, the value may instruct the UE to apply MCS table 3.

8. Information indicating the application of a new MCS table to separateconfiguration parameters for SpCells or SCells for each cell group(ServingCellConfig IE is used to configured (add or modify) the UE witha serving cell, which may be the SpCell or an SCell of an MCG or SCG) orindicating that the application is possible may be included.

A. a downlink BWP list is configured to have a value of 0 or 1 in theServingCellConfig IE, and thus 0 may indicate a downlink BWP to whichMCS table 3 is not applied and 1 may indicate a downlink BWP to whichMCS table 3 is applied. For example, downlinkBWP-ToAddModList MaskSEQUENCE (SIZE (1 . . . MaxNrofBWPs) of BOOLEAN may be included.

9. Information indicating the application of MCS table 3 to individualconfiguration parameters (BWP-DownlinkDediacted) for each BWP of SpCellsor SCells for each cell group or indicating that the application ispossible may be included. For example, the BWP-DownlinkDedicated IE mayinclude NewMCSAllowed BOOLEAN.

After the UE 2 e-01 receives the RRC message (RRC connectionReconfiguration Complete 2 e-65 and 2 e-80) from the BS 2 e-02, the UEoperation proposed when data transmission between the UE 2 e-01 and theBS 2 e-02 is possible is described below.

A. If PHY configuration information (physicalCellGroupConfig) includesMCS-RNTI+list of {BWP id (and CORESET IDs and Search Space IDs), servingcell id} in the RRC message (RRC Connection Reconfiguration in steps 2e-60 and 2 e-75),

-   -   the UE monitors an MCS-RNTI in a place included in the PHY        configuration information.

B. If PHY configuration information (physicalCellGroupConfig) includesMCS-RNTI+list of {BWP id (and CORESET IDs and Search Space IDs,ue-Specific), serving cell id} in the RRC message (RRC ConnectionReconfiguration in steps 2 e-60 and 2 e-75),

-   -   the UE monitors an MCS-RNTI in a place included in the PHY        configuration information.

C. If PHY configuration information (physicalCellGroupConfig) includesonly an MCS-RNTI value and configuration parameters for SCells(ServingCellConfig) includes downlinkBWP-ToAddModList Mask SEQUENCE(SIZE (1 . . . MaxNrofBWPs) of BOOLEAN in the RRC message (RRCConnection Reconfiguration in steps 2 e-60 and 2 e-75),

-   -   the UE monitors an MCS-RNTI in BWPs of serving cells indicated        by the PHY configuration information and ServingCellConfig.

D. If PHY configuration information (physicalCellGroupConfig) includesonly an MCS-RNTI value and individual configuration parameters forSCells (ServingCellConfig) for each downlink BWP (BWP-DownlinkDedicated)includes NewMCSAllowed BOOLEAN in the RRC message (RRC ConnectionReconfiguration in steps 2 e-60 and 2 e-75),

-   -   the UE monitors an MCS-RNTI in BWPs of serving cells indicated        by the PHY configuration information and BWP-DownlinkDedicated.

E. If PHY configuration information (physicalCellGroupConfig) includesonly an MCS-RNTI value and subcarrier spacing (SCS) included in BWPconfiguration information is a specific value, is equal to or smallerthan a specific value, or is larger than or equal to a specific value inthe RRC message (RRC Connection Reconfiguration in steps 2 e-60 and 2e-75),

-   -   the UE monitors an MCS-RNTI in BWPs in serving cells that        satisfy the corresponding condition.

F. If PHY configuration information (physicalCellGroupConfig) includesonly an MCS-RNTI value and periodicity in ConfiguredGrantConfig is equalto or smaller than a specific value in the RRC message (RRC ConnectionReconfiguration in steps 2 e-60 and 2 e-75),

-   -   the UE monitors an MCS-RNTI in BWPs in serving cells that        satisfy the corresponding condition.

G. If PHY configuration information (physicalCellGroupConfig) includesonly an MCS-RNTI value in the RRC message (RRC ConnectionReconfiguration in steps 2 e-60 and 2 e-75),

-   -   the UE monitors an MCS-RNTI in BWPs in serving cells for UL CG        Type 1 configured by the BS.

Information included in the RRC message (RRC Connection Reconfigurationin steps 2 e-60 and 2 e-75) may be also included in an RRC Resumemessage or an RRC Setup message.

FIG. 2F illustrates an operation in which a UE in an RRC-connected modeapplies an MCS table according to an embodiment of the disclosure.

In FIG. 2F, a UE in an RRC-idle mode or an RRC-inactive mode discoversan appropriate cell and camps on the corresponding BS in step 2 f-05,and accesses the BS for the reason of generation of data to betransmitted in step 2 f-10. In the idle mode or the RRC-inactive mode,the UE is not connected to the network to save power of the UE, so theUE cannot transmit data. In order to transmit data, the UE is requiredto switch to a connected mode (RRC_CONNECTED). Camping means that the UEreceives a paging message in order to determine whether data is receivedthrough downlink while staying in the corresponding cell. When the UEsuccessfully performs the procedure of access to the BS, the UE switchesto the connected mode (RRC_CONNECTED), and the UE in the connected modeis able to transmit and receive data to and from the BS.

In the RRC-connected state, the BS transmits RRC connectionreconfiguration to the UE to change MCS-RNTI configuration information,CA configuration information, and CS/SPS configuration information instep 2 f-15.

In step 2 f-20, the UE may perform at least one of the followingdetailed operations.

-   -   Operation of monitoring a C-RNTI in activated serving cells.    -   Operation of monitoring a CS-RNTI for serving cells in which CS        is configured.    -   Operation of monitoring an MCS-RNTI in an activated serving cell        in BWPs configured through the RRC message.

In step 2 f-30, the operation of the UE for applying the MCS table isdescribed below.

-   -   When downlink control information (DCI) is determined as a        C-RNTI (If DCI is addressed by C-RNTI or DCI format with CRC        scrambled by C-RNTI), the UE applies MCS table 2 if an mcs-table        parameter value is configured as qam256 in the RRC message.    -   When downlink control information (DCI) is determined as a        C-RNTI (If DCI is addressed by C-RNTI or DCI format with CRC        scrambled by C-RNTI), the UE applies MCS table 1 if an mcs-table        parameter value is not configured in the RRC message.    -   When downlink control information (DCI) is determined as an        MCS-RNTI (If DCI is addressed by MCS-RNTI or DCI format with CRC        scrambled by MCS-RNTI), the UE applies MCS table 3.    -   When downlink control information (DCI) is determined as a        CS-RNTI (If DCI is addressed by CS-RNTI or DCI format with CRC        scrambled by CS-RNTI), the UE applies MCS table 2 if an        mcs-table parameter value is configured as qam256 in the RRC        message.    -   When downlink control information (DCI) is determined as a        CS-RNTI (If DCI is addressed by CS-RNTI or DCI format with CRC        scrambled by CS-RNTI), the UE applies MCS table 1 if an        mcs-table parameter value is not configured in the RRC message.    -   When downlink control information (DCI) is determined as a        CS-RNTI (If DCI is addressed by CS-RNTI or DCI format with CRC        scrambled by CS-RNTI), the UE applies MCS table 3 if an        mcs-table parameter value is configured as qam64 in the RRC        message.

The embodiment of the disclosure is summarized below.

A new MCS table (MCS table 3) for URLLC has been introduced, and a newRNTI (MCS-RNTI or MCS-C-RNTI) may be configured through RRC in order toactivate the new MCS table.

The new RNTI may be configured through physicalCellGroupConfig withinCellGroupConfig. A common MCS-RNTI is for all cells within a cell group,and a new MCS table may be activated according to RRC configuration.

The embodiment of the disclosure proposes monitoring an MCS-RNTI in aspecific BWP of a specific serving cell configured by RRC in order toreduce processing load of the UE. For HARQ retransmission using the newMCS table, the MCS-RNTI may be used for HARQ retransmission of dynamicallowance/allocation-based initial transmission. Further, the CS-RNTImay be used for HARQ retransmission of configuredallowance/allocation-based initial transmission.

Current RRC Embodiment 1 Refinement #1 Refinement #2 Signaling SignalingSignaling Signaling physicalCellGroupConfig physicalCellGroupConfigServingCellConfig BWP-UplinkDedicated MCS-RNTI MCS-RNTI + list (new)downlinkBWP- (new) NewMCSAllowed Behavior of {BWP id (orToAddModList-Mask BOOLEAN UE monitors MCS-RNTI CORESET ID), servingSEQUENCE (SIZE physicalCellGroupConfig for all BWPs of all serving cellid} (1..maxNrofBWPs)) OF MCS-RNTI only cells Behavior BOOLEAN BehaviorUE monitors MCS-RNTI etc. UE monitors MCS-RNTI for the BWPs of servingphysicalCellGroupConfig for the BWPs of serving cells indicated in theMCS-RNTI only cells indicated in the signaling Behavior signaling UEmonitors MCS-RNTI for the BWPs of serving cells indicated in thesignaling

The table may be interpreted as follows. When the MCS-RNTI is configuredin physicalCellGroupConfig of the current RRC configuration, the UE maymonitor the MCS-RNTI in all BWPs of all cells in the corresponding cellgroup, but it is unnecessary and thus may act as load to the UE.

According to embodiment 1 of the table, not only the MCS-RNTI but alsoat least one piece of identification information of the BWP andidentification information of the serving cell may be included inphysicalCellGroupConfig. A cell for monitoring the MCS-RNTI may beindicated by the identification information of the serving cell, and aBWP for monitoring the MCS-RNTI in the corresponding serving cell may beindicated by the identification information of the BWP. The UE maymonitor the MCS-RNTI in the serving cell and the BWP indicated by theidentification information of the serving cell and the identificationinformation of the BWP. The identification information of the BWP andthe identification information of the serving cell may be configured indifferent fields of the RRC message rather than inphysicalCellGroupConfig, and may be configured through an MAC CE.Further, indication of the serving cell and the BWP through a differentmethod is not excluded.

In the case of refinement #1 of the table, information indicating theBWP is newly added to the configuration of a downlinkBWP ofServingCellConfig. When the MCS-RNTI is configured inphysicalCellGroupConfig, the UE may monitor the MCS-RNTI in a BWP inwhich a Boolean value is configured as True in downlinkBWP-relatedconfiguration information of ServingCellConfig, and may not monitor theMCS-RNTI in a BWP in which the Boolean value is configured as false.

In the case of refinement #2 of the table, a new field may be added toBWP-uplink-related configuration information and a BWP in which theMCS-RNTI should be monitored may be indicated. When the MCS-RNTI isconfigured in physicalCellGroupConfig, the UE may monitor the MCS-RNTIin a BWP indicated through the new field of the BWP-uplink-relatedconfiguration information.

Further, the UE should monitor the MCS-RNTI for a BWP in whichsubcarrier spacing (SCS) has a specific value and monitor the MCS-RNTIin a BWP in which a PUSCH duration time is smaller than the specificvalue. In addition, the MCS-RNTI should be monitored in a BWP in whichtype 1 CG is scheduled.

An ID or a type of a search space may be considered.

The MCS-RNTI may be monitored only for a predetermined search space IDand monitored only for a search space in a UE-specific type.

The embodiment of the disclosure is implemented as follows.

The UE camps on an NR cell. The UE receives RRCReconfiguration mesmessfor a handover. The message may include MCS-RNTI configuration, CAconfiguration, and CS/SPS configuration to be used in a target cell.Further, the message may include the following information.

-   -   physicalCellGroupConfig    -   MCS-RNTI & list of {BWP id (and CORESET IDs and SearchSpace        IDs), serving cell id}    -   SPS-RNTI    -   . . .    -   spCellConfig    -   C-RNTI    -   Target cell info    -   . . . .

The UE transmits a preamble. The UE receives an RAR scrambled with anRA-RNTI. The UE uses MCS table 1 to determine an MCS and the size of aTB. The UE determines the TB size and the MCS for Msg3 on the basis ofMCS table 1. The UE monitors a C-RNTI in an activated serving cell. TheUE monitors a CS-RNTI in a cell in which CS is configured. Further, theUE monitors the MCS-RNTI and the C-RNTI together. The MCS-RNTI may bemonitored in an RRC-configured cell, an RRC-configured BWP, anRRC-configured CORESET, and a UE-specific search space.

Thereafter, the UE receives DCI to be retransmitted. When the DCI isprocessed by the C-RNTI, the UE applies MCS table 1. When the DCI isprocessed by the MCS-RNTI, the UE applies MCS table 3. When the DCI isprocessed by the CS-RNTI and a configured grant is not configured forMCS table 3, the UE applies MCS table 1. When the DCI is processed bythe CS-RNTI and a configured grant is configured for MCS table 3, the UEapplies MCS table 3.

FIG. 2G illustrates a configuration of a UE according to an embodimentof the disclosure.

Referring to FIG. 2G, the UE includes a radio-frequency (RF) processor 2g-10, a baseband processor 2 g-20, a storage unit 2 g-30, and acontroller 2 g-40. The controller 2 g-40 may further include amulti-connection processor 2 g-42.

The RF processor 2 g-10 performs a function for transmitting andreceiving a signal through a wireless channel, such as band conversionand amplification of a signal. That is, the RF processor 2 g-10up-converts a baseband signal provided from the baseband processor 2g-20 into an RF band signal, transmits the RF band signal through anantenna, and then down-converts the RF band signal received through theantenna into a baseband signal. For example, the RF processor 2 g-10 mayinclude a transmission filter, a reception filter, an amplifier, amixer, an oscillator, a digital-to-analog convertor (DAC), ananalog-to-digital convertor (ADC), and the like. Although FIG. 2Gillustrates only one antenna, the UE may include a plurality ofantennas. In addition, the RF processor 2 g-10 may include a pluralityof RF chains. Moreover, the RF processor 2 g-10 may perform beamforming.For the beamforming, the RF processor 2 g-10 may control a phase and asize of each signal transmitted/received through a plurality of antennasor antenna elements. The RF processor may perform MIMO and receive aplurality of layers when performing the MIMO operation. The RF processor2 g-10 may perform reception beam sweeping by appropriately configuringa plurality of antennas or antenna elements according to the control ofthe controller or may control a direction of the reception beam or abeam width such that the reception beam cooperates with the transmissionbeam.

The baseband processor 2 g-20 performs a function for a conversionbetween a baseband signal and a bitstream according to a physical layerstandard of the system. For example, when data is transmitted, thebaseband processor 2 g-20 generates complex symbols by encoding andmodulating a transmission bitstream. Further, when data is received, thebaseband processor 2 g-20 reconstructs a reception bitstream bydemodulating and decoding a baseband signal provided from the RFprocessing unit 2 g-10. For example, in an orthogonal frequency divisionmultiplexing (OFDM) scheme, when data is transmitted, the basebandprocessor 2 g-20 generates complex symbols by encoding and modulating atransmission bitstream, mapping the complex symbols to subcarriers, andthen configures OFDM symbols through an IFFT (inverse fast Fouriertransform) operation and a CP (cyclic prefix) insertion. Further, whendata is received, the baseband processor 2 g-20 divides the basebandsignal provided from the RF processor 2 g-10 in the unit of OFDMsymbols, reconstructs the signals mapped to the subcarriers through anFFT (fast Fourier transform) operation, and then reconstructs areception bitstream through demodulation and decoding.

The baseband processor 2 g-20 and the RF processor 2 g-10 transmit andreceive a signal as described above. Accordingly, the baseband processor2 g-20 and the RF processor 2 g-10 may be referred to as a transmitter,a receiver, a transceiver, or a communication unit. At least one of thebaseband processor 2 g-20 and the RF processor 2 g-10 may include aplurality of communication modules for supporting a plurality ofdifferent radio access technologies. In addition, at least one of thebaseband processor 2 g-20 and the RF processor 2 g-10 may includedifferent communication modules to process signals of differentfrequency bands. For example, the different radio access technologiesmay include an LTE network and an NR network. Further, the differentfrequency bands may include a super high frequency (SHF) (for example,2.2 gHz and 2 ghz) band and a millimeter (mm) wave (for example, 60 GHz)band.

The storage unit 2 g-30 stores data such as a basic program, anapplication, and setting information for the operation of the UE. Thestorage unit 2 g-30 provides the stored data according to a request fromthe controller 2 g-40.

The controller 2 g-40 controls overall operations of the UE. Forexample, the controller 2 g-40 transmits and receives a signal throughthe baseband processing unit 2 g-20 and the RF processing unit 2 g-10.Further, the controller 2 g-40 records data in the storage unit 2 g-40and reads the data. To this end, the controller 2 g-40 may include atleast one processor. For example, the controller 2 g-40 may include acommunication processor (CP) that performs a control for communication,and an application processor (AP) that controls a higher layer such asan application program.

FIG. 2H illustrates a configuration of a BS according to an embodimentof the disclosure.

As illustrated in FIG. 2H, the BS includes an RF processor 2 h-10, abaseband processor 2 h-20, a backhaul communication unit 2 h-30, astorage unit 2 h-40, and a controller 2 h-50. The controller 2 h-50 mayfurther include a multi-connection processor 2 h-52.

The RF processor 2 h-10 performs a function for transmitting andreceiving a signal through a wireless channel, such as band conversionand amplification of a signal. That is, the RF processor 2 h-10up-converts a baseband signal provided from the baseband processor 2h-20 into an RF band signal, transmits the converted signal through anantenna, and down-converts the RF band signal received through theantenna into a baseband signal. For example, the RF processor 2 h-10 mayinclude a transmission filter, a reception filter, an amplifier, amixer, an oscillator, a DAC, and an ADC. Although FIG. 2H illustratesonly one antenna, the first access node may include a plurality ofantennas. The RF processor 2 h-10 may include a plurality of RF chains.Further, the RF processor 2 h-10 may perform beamforming. Forbeamforming, the RF processor 2 h-10 may control phases and sizes ofrespective signals transmitted and received through a plurality ofantennas and antenna elements. The RF processor may perform a downlinkMIMO operation by transmitting one or more layers.

The baseband processor 2 h-20 performs a function of conversion betweena baseband signal and a bitstream according to a physical-layer standardof the first radio access technology. For example, when data istransmitted, the baseband processor 2 h-20 generates complex symbols byencoding and modulating a transmission bitstream. Further, when data isreceived, the baseband processor 2 h-20 reconstructs a receptionbitstream by demodulating and decoding a baseband signal provided fromthe RF processor 2 h-10. For example, in an OFDM scheme, when data istransmitted, the baseband processor 2 h-20 may generate complex symbolsby encoding and modulating the transmission bitstream, map the complexsymbols to subcarriers, and then configure OFDM symbols through an IFFToperation and CP insertion. In addition, when data is received, thebaseband processor 2 h-20 divides a baseband signal provided from the RFprocessor 2 h-10 in units of OFDM symbols, recovers signals mapped withsubcarriers through an FFT operation, and then recovers a receptionbitstream through demodulation and decoding. The baseband processor 2h-20 and the RF processor 2 h-10 may transmit and receive signals asdescribed above. Accordingly, each of the baseband processor 2 h-20 andthe RF processor 2 h-10 may be referred to as a transmitter, a receiver,a transceiver, a communication unit, or a wireless communication unit.

The communication unit 2 h-30 provides an interface for communicatingwith other nodes within the network.

The storage unit 2 h-40 stores data such as a basic program, anapplication, and configuration information for operating the MeNB.Particularly, the storage unit 2 h-40 may store information on bearersallocated to the accessed UE and the measurement result reported fromthe accessed UE. Further, the storage unit 2 h-40 may store informationthat is a reference for determining whether to provide multipleconnections to the UE or stop the connections. The storage unit 2 h-40provides stored data according to a request from the controller 2 h-50.

The controller 2 h-50 controls the overall operation of the MeNB. Forexample, the controller 2 h-50 transmits and receives a signal throughthe baseband processor 2 h-20 and the RF processor 2 h-10 or through thebackhaul communication unit 2 h-30. Further, the controller 2 h-50records data in the storage unit 2 h-40 and reads the data. To this end,the controller 2 h-50 may include at least one processor.

The embodiments of the disclosure described and shown in thespecification and the drawings have been presented to easily explain thetechnical contents of the disclosure and help understanding of thedisclosure, and are not intended to limit the scope of the disclosure.Therefore, the scope of the disclosure should be construed to include,in addition to the embodiments disclosed herein, all changes andmodifications derived on the basis of the technical idea of thedisclosure.

What is claimed is:
 1. A method performed by a terminal in a wirelesscommunication system, the method comprising: receiving, from a basestation, a first radio resource control (RRC) message including firstinformation associated with a reconfiguration with synchronization andsecond information associated with a signaling radio bearer (SRB) list;identifying whether a first indicator associated with a reestablishmentof packet data convergence protocol (PDCP) data, a second indicatorassociated with a discard on PDCP data, or a third indicator associatedwith a recovery of PDCP data is included in the second information;performing an operation of the recovery of PDCP data for at least oneSRB associated with the third indicator, in case that the thirdindicator associated with the recovery of the PDCP data is included inthe second information; and transmitting, to the base station, a secondRRC message as a response to the first RRC message.
 2. The method ofclaim 1, further comprising: performing an operation of thereestablishment of PDCP data for at least one SRB associated with thefirst indicator, in case that the first indicator associated with thereestablishment of PDCP data is included in the second information,wherein the operation of the reestablishment of the PDCP data includesdiscarding all data stored in the at least one SRBs associated with thefirst indicator, initializing a window status parameter for the at leastone SRBs associated with the first indicator, and resetting a timer foralignment for the at least one SRB associated with the first indicator.3. The method of claim 1, further comprising: performing an operation ofthe discard on PDCP data for at least one SRB associated with the secondindicator, in case that the second indicator associated with the discardon PDCP data is included in the second information, wherein theoperation of the discard on the PDCP data includes discarding all datastored in the at least one SRBs associated with the second indicator,initializing a window status parameter for the at least one SRBsassociated with the second indicator, and resetting a timer foralignment for the at least one SRB associated with the second indicator.4. The method of claim 1, further comprising: identifying first datarelated to a transmission for the recovery of PDCP data among datastored in the at least one SRB which is configured before receiving thefirst RRC message; and transmitting the first data to a lower layer,wherein the first data includes data of which successful transmission isnot identified among data transmitted to a reestablished RLC layerdevice or a connection-released RLC layer device.
 5. The method of claim1, further comprising: identifying second data related to a receptionfor the recovery of PDCP data among the data stored in the at least oneSRB which is configured before receiving the first RRC message;processing the second data; stopping a timer for alignment in case thatthe timer is running for the at least one SRB; and resetting the timerfor alignment.
 6. The method of claim 1, wherein the recovery of thePDCP data is related to a case in which a handover having no change in aPDCP security key is instructed to the terminal, wherein the handoverhaving no change in the PDCP security key includes a handover having nochange in a central unit (CU) but having a change in a data unit (DU),and wherein the reestablishment of the PDCP data is related to a case inwhich a handover having a change in a PDCP security key is instructed tothe terminal.
 7. The method of claim 1, wherein the first RRC messagefurther includes a fourth indicator indicating whether to use a previousheader compression protocol, and wherein a header compression protocolis reset in case that the fourth indicator is not included in the firstRRC message.
 8. The method of claim 1, wherein the operation associatedwith the recovery of the PDCP data is performed in case that the atleast one SRB associated with the third indicator is established beforereceiving the first RRC message and the second information includes thethird indicator.
 9. The method of claim 1, wherein the first RRC messageindicates a type of a specific RRC message for retransmission, andwherein the specific RRC message is for a retransmission of at least oneof RRC message which is transmitted before receiving the first RRCmessage.
 10. A method performed by a base station in a wirelesscommunication system, the method comprising: transmitting, to aterminal, a first radio resource control (RRC) message including firstinformation associated with a reconfiguration with synchronization andsecond information associated with a signaling radio bearer (SRB) list;and receiving, from the terminal, a second RRC message as a response tothe first RRC message, wherein an operation of a reestablishment ofpacket data convergence protocol (PDCP) data for at least one SRBassociated with a first indicator, in case that the first indicatorassociated with the reestablishment of PDCP data is included in thesecond information, wherein an operation of a discard on PDCP data forat least one SRB associated with a second indicator, in case that thesecond indicator associated with the discard on PDCP data is included inthe second information, and wherein an operation of a recovery of PDCPdata for at least one SRB associated with a third indicator, in casethat the third indicator associated with the recovery of PDCP data isincluded in the second information.
 11. A terminal in a wirelesscommunication system, the terminal comprising: a transceiver; and acontroller configured to: receive, from a base station, a first radioresource control (RRC) message including first information associatedwith a reconfiguration with synchronization and second informationassociated with a signaling radio bearer (SRB) list, identify whether afirst indicator associated with a reestablishment of packet dataconvergence protocol (PDCP) data, a second indicator associated with adiscard on PDCP data, or a third indicator associated with a recovery ofPDCP data is included in the second information, perform an operation ofthe recovery of PDCP data for at least one SRB associated with the thirdindicator, in case that the third indicator associated with the recoveryof the PDCP data is included in the second information, and transmit, tothe base station, a second RRC message as a response to the first RRCmessage.
 12. The terminal of claim 11, wherein the controller is furtherconfigured to perform an operation of the reestablishment of PDCP datafor at least one SRB associated with the first indicator, in case thatthe first indicator associated with the reestablishment of PDCP data isincluded in the second information, and wherein the operation of thereestablishment of the PDCP data includes discarding all data stored inthe at least one SRBs associated with the first indicator, initializinga window status parameter for the at least one SRBs associated with thefirst indicator, and resetting a timer for alignment for the at leastone SRB associated with the first indicator.
 13. The terminal of claim11, wherein the controller is further configured to perform an operationof the discard on PDCP data for at least one SRB associated with thesecond indicator, in case that the second indicator associated with thediscard on PDCP data is included in the second information, wherein theoperation of the discard on the PDCP data includes discarding all datastored in the at least one SRBs associated with the second indicator,initializing a window status parameter for the at least one SRBsassociated with the second indicator, and resetting a timer foralignment for the at least one SRB associated with the second indicator.14. The terminal of claim 11, wherein the controller is furtherconfigured to: identify first data related to a transmission for therecovery of PDCP data among data stored in the at least one SRB which isconfigured before receiving the first RRC message, and transmit thefirst data to a lower layer, wherein the first data includes data ofwhich successful transmission is not identified among data transmittedto a reestablished RLC layer device or a connection-released RLC layerdevice.
 15. The terminal of claim 11, wherein the controller is furtherconfigured to: identify second data related to a reception for therecovery of PDCP data among the data stored in the at least one SRBwhich is configured before receiving the first RRC message, process thesecond data, stop a timer for alignment in case that the timer isrunning for the at least one SRB, and reset the timer for alignment. 16.The terminal of claim 11, wherein the recovery of the PDCP data isrelated to a case in which a handover having no change in a PDCPsecurity key is instructed to the terminal, wherein the handover havingno change in the PDCP security key includes a handover having no changein a central unit (CU) but having a change in a data unit (DU), andwherein the reestablishment of the PDCP data is related to a case inwhich a handover having a change in a PDCP security key is instructed tothe terminal.
 17. The terminal of claim 11, wherein the first RRCmessage further includes a fourth indicator indicating whether to use aprevious header compression protocol, and wherein a header compressionprotocol is reset in case that the fourth indicator is not included inthe first RRC message.
 18. The terminal of claim 11, wherein theoperation associated with the recovery of the PDCP data is performed incase that the at least one SRB associated with the third indicator isestablished before receiving the first RRC message and the secondinformation includes the third indicator.
 19. The terminal of claim 11,wherein the first RRC message indicates a type of a specific RRC messagefor retransmission, and wherein the specific RRC message is for aretransmission of at least one of RRC message which is transmittedbefore receiving the first RRC message.
 20. A base station in a wirelesscommunication system, the base station comprising: a transceiver; and acontroller configured to: transmit, to a terminal, a first radioresource control (RRC) message including first information associatedwith a reconfiguration with synchronization and second informationassociated with a signaling radio bearer (SRB) list, and receive, fromthe terminal, a second RRC message as a response to the first RRCmessage, wherein an operation of a reestablishment of packet dataconvergence protocol (PDCP) data for at least one SRB associated with afirst indicator, in case that the first indicator associated with thereestablishment of PDCP data is included in the second information,wherein an operation of a discard on PDCP data for at least one SRBassociated with a second indicator, in case that the second indicatorassociated with the discard on PDCP data is included in the secondinformation, and wherein an operation of a recovery of PDCP data for atleast one SRB associated with a third indicator, in case that the thirdindicator associated with the recovery of PDCP data is included in thesecond information.